Samarin is a company specialized in the construction of connecting rods and crankshafts and they are based in Spain. They undertake the development of stock conrods as well as custom ones.
Here is an example of a special conrod that allows the use of later NX4 pistons on Honda Rs125 NF4 bikes. This conrod has 105mm centers (stock is 104mm) and uses a 15mm wrist pin (stock is 14mm) hence later NX4 pistons can be used in pre'95 era Rs125 bikes without any cylinder modifications.
I believe Samarin also constructs connecting rods for the Honda Nsr250 bike but Tuck(NZ) knows a lot more than me about this subject, so check out his post at edetuckracing.blogspot.com.