One problem with looking for 2nd hand parts is the wheels are not your usual QR front and rear. Well your front could be QR depending on your fork but I would strongly recommend against a QR front on a Rocket!
This does make it harder. You could go with some Superstar Switch hubbed wheels – like Hope but not quite and won’t have the price tag.
Forks – either a Merlin deal or 2nd hand. Stem, seat post etc – hit the classifieds for some nice Thomson stuff. Bars – lots of bargains on CRC for something >700mm.
For drivetrain I am guessing you want 2×10 or maybe 1×10? Not sure what 10 speed stuff is hitting the classifieds but tbh I would go for one of the new shadow+ XT rear dérailleurs.
Brakes + rotors – definitely hit the classifieds.
Don’t forget to allow for cables etc.
Headset – it’s 44mm isnt it so again quite rare for used ones. Either check out CRC etc for a clearance bargain, opt for the default Hope (I would) or look at superstar (mine has been fine and they stock spares which is nice to know you can get them)