Great amateur radio spare parts and good offers for ham radio amateurs – especially for OMs on the microwave bands -can be found at:
Kuhneelectronic on EBAY: https://www.ebay.de/sch/kuhneelectronic/m.html?item=151623156096&hash=item234d71c180&pt=LH_DefaultDomain_77&rt=nc&_trksid=p2047675.l2562
hamradiospareparts on EBAY: https://www.ebay.de/sch/hamradiospareparts/m.html?_nkw=&_armrs=1&_ipg=&_from