Your only option for a replacement shell is to find someone who understands a married Accessport is worth nothing (since it costs 70% to relicense, which is the same cost or more you can buy a used one for), and see if they'll sell it to you for like $20. I have a replacement shell you can have for free if you want, but the clear screen plastic is cracked and the back has a couple scratches. I'll upload some pics in a bit. But, I'll send it to you for nothing if you want it.
One thing to keep in mind if it matters to you, is your serial number is attached to the shell, so if you replace the front part of the shell, the s/n won't match.
Also, that's a pretty nice mount solution, would you be willing to share the stl?