If you can't find a transmitter (I had one back in the 80's but it died and was tossed in the garbage), another solution is to use an Agile Modulator as a transmitter.
I hope it's OK to share links here. This guy has a full writeup on one way to do it:
https://antiqueradio.org/HomeTVTransmitter.htm
Links are acceptable
When I first started looking for a solution I found the site you linked too. I spent the next few years looking for the same set up as him, to no avail. I found similar equipment for big money. I think he may have just gotten lucky on what he paid on eBay. Most of this old TV test equipment goes for big money. My little transmitter does the same thing for cheap, but of course, if you find another solution, go for it!
What ever gets that old blaster off the shelf!