Your model 115 will take a regular class 15 slide plate, tap in spool pin and regular 15x1 needles. The parts are readily available. I purchased mine from Sewclassic. Same for the treadle belt. The bobbins are an "L" type also available from Sewclassic. I am sure that there are other vendors that sell the parts you need, but I have always been happy with Sewclassic's prompt service.