Have a look at:
https://www.51-factory.com/inventory.htm and
https://retrotrackandair.com/aero-en...ce-department/. Places like this, and there are more, can deliver a lot of what the warbird movement needs. Some exotic engines and engine variants can be challenging... but so far a lot of issues have been sorted out and as you say, the Merlin engine situation does not appear to be a constraint here.