Young man, Although I thank you for the confidence you're putting in me, many MANY people here on the forum know about the old Heng Long electronics, because we're all old
If you look within your battery compartment, do you have something that has a number on it, like 01, because depending on whether you do or don't, will let us know one of the two possible Tx's you'll need.
Sadly any electronics you purchase as a whole package will be from about the same price your tank was originally, to easily twice or three times what the whole tank cost.
But I'm sure you can get just the transmitter for under £20