Make sure the locating dowel is in place between the crankcase and oil pipes bolt on block. Without it the block can move and obstruct the oilways. Nothing special about the rest of the fittings, my bike came with homespun PVC oil connection pipes straight from the hardware store......these days there is a bit more choice. Any oil resistant flexible tube to fit the metal tubes will do, car fuel injection hose is fine, and being reinforced maybe a bit more durable, tho' there is no great pressure in the return. Hose with metal braid outer for extra bling maybe and clips to suit.
Swarfy.