Yes, I had problems with availability of med 30 mm steel rings from TPS... ordered in Nov 2016 (backordered)... 5 months later, canceled the order and went with Leupold Mark 4 (high) (1.06") and was very happy with them. The TPS rail that I was lucky enough to get (it was in stock) when I made the original order had 4 6-48 screws that were all the same length... in my Rem 700 SA, the front screw hole is shorter than the other 3!... some manufacturers (Badger) seem to understand this and provide appropriate screws (1 shorter)... but not TPS. When I called them about the issue, they were lost... and suggested stupid/expensive solutions. They did not have a short 6-48 anywhere. I was left twisting in the wind. Now this wasn't the world's biggest problem but I expected better customer service. I ended up shortening the screw myself and I was lucky enough not to botch it completely. When I mentioned the 5 month backorder on the rings that I wanted, I was told that the steel ones are less popular and that they are only made in short "runs"... but fortunately, they were scheduled to run another batch soon. In addition, it seems that Midway USA is their largest vendor and gets priority when it comes to orders and shipments... so if you are stuck on TPS, watch Midway. Midway seems to have 34 mm steel Leupold Mark 4 rings @ $150
here. SWFA seems to have the steel 34mm "High" (1.10") Mark 4 rings for $142... Their website is doing maintenance and isn't fully functional (when I am writing this) so I can't tell you more... you will have to look later if you want to go that route...
Best of luck with your project!
- r -