all parts available from tyga. crank, pistons, cylinders, heads, gaskets and what not. MC21/28 crank will need milling modification to fit MC18 R5K cases however. MC18 cranks no longer available. shipping does not take long even from the other side of the world. but you'll pay for it.

count yourself lucky. A MC21/28 crank will not fit into an MC18 R2J case.
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MC21R9N track
MC18R2J track
CBR954
CR250