Soft Shell Crab Sandwiches can be had in Arlington at America's Seafood, which is behind the shopping strip where Lee Hwy splits (same one with Arrowine). It is a fish market that also offers some prepared foods, with a couple of tables outside.
I haven't had the sandwich at Breadline so can't compare, but this one is fine. Since the bread is a standard small sub role, that wouldn't match up to breadline, but the soft shell comes from the case and is only breaded and prepared when you order. The soft shells there are very fresh (at least when I've bought them).
Comes with fries and cole slaw.