Hard to find parts are:
1. Replacement chassis
2. Belts.. V1 in particular

all other bits are more or less interchangeable and upgradable with later cars.. eg you can use suspension arms from 418, 419, 420 with no issues.

Belt, you can switch to V2 belt if you change the pulleys, which is better anyways. V2 belts can still be found.

Hop Up.. there is still plenty of inventory out there