Where are the agrarian reforms of Basil II codified?

First of all, the Nomos Georgikos is not a set of laws issued at one point in time. This collection resembles much the history of the bible in sofar as the laws have been assemled – and changed, in extent, in content – from 740–14th century. Beginning at Leo III the Isaurian (717–741). Only at that late time it somewhat solidified into a canon-like collection.

J. Karayannopulos: "Entstehung Und Bedeutung Des Nomos Georgikos", Byzantinische Zeitschrift, Volume 51, Issue 2, 1958. (DOI)

Compared to Wikipedia: Byzantine_law#The_Farmer's Laws

An important source regarding law, which reflects in a particularly characteristic way the internal life of the Byzantine villages during the Middle Byzantine Era (7th – end of 12th century) is the Nomos Georgikos, also known as the Lex Rustica or Farmer's Law. Due to its importance, the Farmer's Law roused the interest of researchers from a very early stage. Ever since it has been one of the most discussed texts concerning the internal history of Byzantium. […] It is a private collection, continuously enriched, and refers to specific cases relevant to rural property within the framework of the Byzantine rural "community". As evident by the dispositions of the "Law", peasants were organized in "communities" and collectively responsible for the payment of the total tax the "community" was liable for, being obliged to pay as well the amounts corresponding to indebted members of the community. As for the chronology of its writing, since the text itself bears no specific date, it is placed somewhere in between the second half of the 6th century and the middle of the 14th.

Now, the specific laws of Basil II regarding agricultural policy were an alteration and addition to the Nomos Georgikos or Farmer's Law, coinciding in time of issue with the time/dating of manuscripts we do have:

(Νόμος Γεωργικός), a legal text preserved in dozens of MSS from the end of the 10th C. onward.
OUP Dictionary of Byzantium

This situation was part of practical necessity:

The need for translation and simplification resulted in the enactment of new official codes in the so-called “dark ages” (7th–9th centuries) in Byzantium, such as the Ekloga legum of the Isaurians in the 8th century and three thematic law codes: the Military Code (Νόμος στρατιωτικός), the Rhodian Maritime Code (Νόμος Ροδίων ναυτικός), and the Farmer’s Law (Νόμος γεωργικός). These law codes were enacted for practical purposes in a society which was changing rapidly; they became digests for practical use by non-specialists. One of the reasons for these changes was the Barbarian invasions, which significantly changed the demographics of the empire. The Nomos Georgikos (NG), which is part of the post-Justinianic legis- lation, addresses only one category of inhabitants: peasants. It is generally held that the NG was composed, or at least enacted at the end of the 7th or at the beginning of the 8th century AD. Nevertheless, it was probably in general use in the 9th century AD.7 e rules in the code are common, the terminology for the rural classes is almost monolithic, and the code can be related to any period and place, because its terseness doesn’t allow de nite conclusions about the context.

Daniela Toševa-Nikolovska: "Some Observations on the Nomos Georgikos", Colloquia Humanistica 7 (2018) (DOI)

An extract of a translation into English of an early version is online:

Fordham University, Internet Medieval Source Book, The Farmer's Law, 7-8th Centuries from W. Ashburn:r (trans.), "The Farmer's law", Journal of Hellenic Studies, 32 (1912), 87-95.

The aforementioned disputed details of the history of this collection makes finding a definitive manuscript quite futile. However a recent critical edition (which ironically met met praise for the collection and translations but criticism for the conclusions presented en passant) would be:

Vizantijskij Zemledel’českij Zakon, von I. P. MEDVEDEV (Greek Text), E. K. PIOTROVSKAJA (old-Russian translation) and E. E. LIPšIC (Commentary), Leningrad 1984; cf W. Ashburner, The Farmers Law, The Journal of Hellenic Studies 30, 1910, 85 ff, (= ΖεPOI, JGR Bd. II, 63‒71, where [S.VΙΙΙ] all previous editions are listed in detail).

Cited from: Spyros Troianos: "The Sources of Byzantine Law" (ΤΡΩΙΑΝΟΣ ΣΠΥΡΙΔΩΝ: Οι Πηγές του Βυζαντινού Δικαίου, Τρίτη έκδοση συμπληρωμένη)(German Version)

If the focus should be the specific reforms of Basil II, then you would have to look at 'novellas' to the laws. These are as well listed in Troaionos, plus papers on them like:
Franz Tinnefeld: "Zur Novelle Basileios’ II. gegen den Landerwerb der Mächtigen im Bereich der Dorfgemeinden (1.1.996)", in: P Schreiner & O Strakhov (Eds): "Χρυσαι πυλαι – Zlataja vrata. Essays presented to Ihor Sevcenko on his eightieth birtday by his colleagues and students" vol 2. Palaeoslavica 9,2, Cambridge Mass, 2002, p 248–256. [On the novella of Basileios' II. against the acquisition of land by the powerful in the area of the village communities.]