I considered making one too. But dropped the idea of making a 7mm LRM when I found out that Gunwerks had exclusive rights to the reamer. I like to own my reamers made to my specifications.
I ended up making a 7mm/375 Ruger by just necking down the case with no shoulder movement.
Necking down from 375 to 338 was quite easy. I used a Hornady 338 RCM FL die. (the 375 Ruger and 338 RCM share the same shoulder angle and diameter) I also have a whidden 338 RCM FL bushing die. It was simply a matter of stepping down through various bushings to get to 7mm. This solved the first issue on being able to make the brass.
I then talked to Dave Kiff at Pacific Tool and Gauge. I knew others had Dave make them a reamer when the 375 Ruger first came out. I asked about the short neck being an issue and he said it wasn't so I had him make me a .317 neck 7mm/375 Ruger reamer.
I did have to turn the necks and chose .013" neck wall thickness.
I rechambered two rifles for this new cartridge and have had zero issues. More on the rifles later.
For dies I decided to try and use stuff I had on hand. I reamed the allignment tube inside a 7mm rem Redding comp die with my reamer for seating. Currently using Whidden 338 RCM FL bushing die for neck sizing. Using a 375 Ruger FL die for body taper. Haven't had to push shoulders back with twice fired brass but when needed I'll use the 338 RCM die for that. So far I am getting low runout.
More importantly I am getting excellent accuracy with both rifles.
First rifle is a Mark X in a McMillan with a short 7 rem mag barrel. It is a setback 7mm Rem takeoff that is 23 1/4" long. The other is a 11 lb Mark X in a Russo stock with a 30" 1 in 9 twist fluted SS lilja 6 groove 7 STW takeoff a friend sold me with 200 rnds through it. It is now 29 3/8".
Both rifles shoot the 180 Bergers.
Short barreled rifle uses moly coated 180 VLD hunting with 84 grs of RL-33 vel 3075 fps
Long barreled rifle uses 180 hybrid target with 83 gr of RL-33 vel 3200 fps.
I am happy with this fun experiment. I am currently trying other combinations with the short barreled rifle. I am certain I'll burn it out with other loads but don't worry as I have three more 7mm rem mag takeoffs I can install. I do all this work myself and it is lots of fun.
I suppose you could try to get Gunwerks to allow you to buy a reamer but I'll bet they won't do it. Why should they? They will chamber a rifle you send them. Once you do that you can buy the dies and brass.
Let us know if they allow you to get one of their reamers.