How handy are you with coming up with your own solutions? I used a valve like this:

https://www.summitracing.com/parts/fss-74828?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-four-seasons&gclid=CLTNgsmhmc8CFdgPgQodxigHQQ

I needed to also purchase an elbow and a throttle cable to fabricate the parts. I found the valve to work pretty well.

One of my older posts on BB described how to do this. However, in that post I had used an old VW valve which didn't hold up. Most of the procedure is the same though using the above valve. I installed the above valve horizontally rather than vertically.

Here is the link to my old post. The pictures got lost but they are reposted at the end of the thread.

https://www.brickboard.com/RWD/volvo/1471359/220/240/260/280/cheap_heater_valve_replacement.html