Someone posted elsewhere that some of the Ironsighter scope mounts for TC guns are made to fit the existing sight holes. Details are lacking on the Ironsighter website but you can give them a call and ask.

Ironsighter Co., Westland, MI - phone 734-326-8731

Here's their scope mount listings for TC models:

http://www.ironsighter.com/c-188-thompson-center.aspx