You are going to be out of luck for a complete build. Most manufacturers don't want to jump through the hoops of making a specific HBAR model just for one state.
However, if you are going PSA, their lowers are cheap-get that (they transfer as "other", not a rifle) and then get one of their pistol build kits (lower parts kit, buffer and "brace" of choice, and complete upper of choice). Its very affordable. Then its just a few minutes of assembly at home with youtube/minimal tools, or go to a gunsmith and you should be good to go. No need to worry about HBAR at all.
There are plenty of MD compliant (HBAR) AR’s available for sale in MD from different manufacturers.
Ruger, Windham, LWRC, and Colt to name a few.
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