All parts available for all HS and Creos airbrushes at spraygunner.com
If it's out of stock (temporarily) but you need it like here and now, our brave customer support team will tear apart the same airbrush and pull out the part you need (truth, done MULTIPLE times, I can tell by the number of airbrushes on a service desk with a sticker "missing that"). Everybody had some supply chain issues in 2020 so we had to strip a lot of brushes.
Speaking of HS: in general, I agree about Ultra. Probably PS289 or PS270 will serve you better. But when it comes to Infinity, I'm a big fan of their universal design. Super easy to disassemble and clean, no chance to break nozzle when assembled/disassembled since no wrench needed, up to 50ml cup can be installed and up to 0.6mm nozzle. And with Infinity FIne Line air cap, 0.4mm serves as a "detail" nozzle and allows pretty amazing details which simply impossible with other 0.35-0.4mm airbrushes.