you said, "how hard is it to get spare parts for a comparable Glock 9mm vs the .40?" If for example it's a G22 Gen 3, the parts of a Glock 19 Gen 3...almost all internal parts can be had. But if you're worried start buying up parts. There's a parts store that sells a lot of parts for Gen2-Gen5. Can I mention the website here?A .40 is the last caliber I'd buy in today's world. Couple years ago the market was flooded with police department trade ins and people offloading .40's left and right. The popularity of that caliber is dying off, which means the supply, variety, and availability of the ammo will drop off with time. If you're buying a gun knowing you'll never shoot more than 500 rounds through it then you'd probably be fine. If this is going to to get used in training classes or actually practiced with using live ammo then just stay away from .40. Nothing wrong with the caliber on any level of performance, it's a matter of logistics that makes me wonder a guy would want the headaches. For example, how hard is it to get spare parts for a comparable glock 9mm vs the .40? Today it's one situation, in three years it may be a completely different situation.