The external thread dimension will match with Opticron zoom eyepieces but as binastro says, the question is whether the Tasco you have is metric or imperial. The chances of finding a second hand imperial thread zoom are slim to none.
There may be some ex-demo or otherwise used zoom eyepieces in our US stock - you could contact my colleague Kyla Burgess at [email protected]
and she can let you know what she has available. Your risk would be the cost of postage both ways.