I think I finally found one. I found it at IMA-USA. They had it listed as a M1 Thompson jump bag but I think it’s actually for the Reising. The description said that it was for a M1 Thompson with the stock removed. I think that is inaccurate since when the Para-Marines were really a thing I don’t think the Marines had many M1 Thompson’s and it says that the stock had to be removed from the Thompson to fit. Assuming that with the stock removed, a M1928A1 and M1 are relatively close in length (minus the Cutts of course) I think the bag is too short for a Thompson to fit. The Reising however, fits perfectly. I’ve been looking for one of these bags for close to six years.
More photos: https://imgur.com/a/SM2mWmj