Piston rings

I need piston rings for a Murray M2500, 41ADZ01C78. I accidentally broke one of them. the new machine cos about $70 so I don't need a new block. I found the reason it wouldn't start the kill switch wire was shorted. The machine has very little use so I hate to throw it away . Can anyone tell me where I can get rings. I have the ring specs piston is 1.3750" groove is .0055 deep,the ring is inside to outside .0630 and top to bottom .0480.I think it is cast iron 

What size bore do you have in MM? it appears you are looking at a 35mm x 1.2mm ring. Will need an image of the tips to see have are made to see if the 725R rings will work or not.
 
Now as Roy said MTD doesn't want repairing these trimmers. They buy them so cheap that they won't even brother selling the parts. This is why many of us repair shops no longer accept anything that sold for under 100 usd.