score:5
There is no publicised source for these that I am aware of. I know that in Amadeus if you perform a MasterPricer search they return the original RBDs along with the mapping to Cabin Classes for the fares that are returned, so the database can be built up this way. If you have access to a GDS then you can likely get this information out of there.
If you need this for just one Airline then I'm happy to submit them on here, if you need it general then you will need to get this out of a GDS or collect individually from each airline.
For EK/EY:
RBD AirlineCode CabinClass
A EK First
B EK Economy
C EK Business
D EK Business
E EK Economy
F EK First
G EK Economy
H EK Economy
I EK Business
J EK Business
K EK Economy
L EK Economy
M EK Economy
N EK Economy
O EK Business
P EK Business
Q EK Economy
R EK Economy
S EK Economy
T EK Economy
U EK Economy
V EK Economy
W EK Economy
X EK Economy
Y EK Economy
Z EK First
A EY First
B EY Economy
C EY Business
D EY Business
E EY Economy
F EY First
G EY Economy
H EY Economy
I EY Economy
J EY Business
K EY Economy
L EY Economy
M EY Economy
N EY Economy
O EY Economy
P EY Economy
Q EY Economy
R EY First
S EY Economy
T EY Economy
U EY Economy
V EY Economy
W EY Business
X EY Business
Y EY Economy
Z EY Business