There are broken MC250s listed on eBay now and then - good for parts.http://www.ebay.com/itm/Mcintosh-MC-250 ... 720wt_1270
There are also people who sell repair/restoration services - you could ask them if they have the part:http://www.ebay.com/itm/RESTORATION-SER ... 282wt_1270
Disclaimers: I'm happy to share whatever relevant gear knowledge or experience I have. Genuflection/payment/proof of worthiness neither sought nor accepted. I don't design, build, market, sell or endorse for pay any new music product or service. I occasionally sell personal used gear. I am an unpaid endorser of SoundScaper Productions and Godfrey Daniels Guitarworks.