Recently my 27MHz. Train Engineer stopped working. I looked and telephoned the well known UK retailers and managed to get a second hand TE Tx plus Rx from Sandy at Scottish Garden Railways.
I did investigate why my original TE had failed and it was simply due to the AA batteries giving off fumes as they were expiring. A careful clean with a soft tissue over both sides of the pcb and components removed the "film" and brought the TE back to life.
I had intended to look for a s/hand TE: the failure prompted me into action.
This all turned out to be fortunate as it meant that my three existing receivers still had a purpose and were not going to be redundant and I now have a second transmitter and fourth receiver. The fourth Rx is used to control track power, when used, the other three are fitted into battery trailing cars.
The other option, had I not found the s/h TE Tx and Rx. would have been to opt for the Crest Electronics Revolution. Obviously this would have been a more expensive option that the s/h TE. Some REVO's are still available in the UK, I notice, but they are also easily imported direct from Crest in New Jersey.