125-200cc FBF 133, where to get parts??

2007 CR125 with the FBF 133 head. Have not pulled the top off yet, but was trying to figure out
where to get parts before the work started. Is it just a matter of measuring the bore and old piston and checking what was stamped on it? Or should I be thinking of something else?
Thanks,

I have a good condition used fbf 135 top end I would sell you

Call FBF Ferracci in PA...they made them. they may have a piston and rings around.

Weisco cam make a 56mm piston for you.

I've offered a new piston with no response

Thanks for the responses guys.
I will let the wife run it for the next month then our season wraps up.
Then off with its head and lets see what we got.
Sent a message to Ferracci in PA for info.
- rockdancer thank you for the offer, I think the shipping might double the price!

Shipping isn't that dear 25?
I'd like try a fbf 135 . I liked my fbf125
If you decide to go 144 I may be interested in the cylinder
The other option is to go to 165