Upvote:2
A good luggage repair shop can often work magic, including replacement wheels that may not be original, but will fit. Sometimes people will even replace the wheels with inline skate wheels in advance for more durability. (Note that this doesn't usually work with the "spinner" style bags, which usually have much more fragile wheels.) Before getting a whole new bag, it's worth seeing what a repair shop can do.
If you travel often enough for broken luggage to be a considerable problem, it likely makes sense to invest in high quality luggage with a long warranty. Good luggage manufacturers sell wheel/axle kits (see, for example, parts options for Travelpro), so you might pick some parts up in advance so you're not caught short if they're no longer available in the future. Briggs and Riley bags aren't cheap, but have parts kits for wheels available for a nominal fee in addition to the regular repair options. Red Oxx doesn't make bags with wheels, but has a very strong lifetime warranty.
Choosing a very common model, or even one of the models typically used by flight crew will help ensure the availability of repair options in the future.