Thetford Norcold bought Tecma several years ago...send it to them. Their website is a disaster to try to find anything, but several Tecma toilets are included in the list of toilets on this page:
And in the left hand column on that page you'll find the words "service centers."
If THAT doesn't help, try Peterson Marine
PH: 813 854 2252
They're the largest Tecma dealer on the east coast