250-500cc 360 cylinder sleeve

Hi,
I am renovate a 360cc 93', incl- frame paint, plastics renew etc.
As part of it i am rebuilding the head and not sure about the cyl size (it has "D" engraved on it).
I'm wonder if it's possible to find new cyl sleeve or and start from the smallest piston again.
Promise to put some pics in the end.
THX.

Give LA Sleeve or Northwest Sleeve a call. They can build you a custom one if they don't have one in stock.

Any international number/website?

is the cylinder damaged?
this is a nikasil engine, the piston sizes are incremental for initial production, they are within a couple of thousands of each other in size
if you have no damage just look at the piston and maybe if it's good you only need rings, if the cylinder is damaged get it repaired
the reason for nikasil was heat dissipation and the original cylinders are tough, hear of couple hundred hours with one ring change in the middle

No damage,
Both cyl & piston looks ok.
I have the beast for 2 years now and i am not sure how many pistons already been replaced.

Your best avenue is grab a Wossner 'A' piston and get the cylinder re-nikasil back to OE specs....if you are at the 'D' piston then the cylinder and piston is at it's absolute limit (unless you get a custom piston to suit a worn bore) as this is a .50 overbore...haven't seen a size letter on a cylinder (could be wrong or that's a manufacturers stamping) but your best bet is to measure the cylinder about 10mm from deck height with a micrometer focusing on left right, front back then measure the piston and lookup the Wossner site for the piston size as this will indicate what piston size you have OR spray the top of the piston with brake cleaner, let it soak, then scrub to reveal the piston part number:
Wossner size and part numbers are:
77.94 - Kit Part No. 8076DA
77.95 - Kit Part No. 8076DB
77.96 - Kit Part No. 8076DC
78.44 - Kit Part No. 8076D050

Why Wossner? They are the OEM piston's for all WR360's.

then replace the ring and keep going
don't fix it if it ain't broke