I didn't have any success for my quest for street legal* chem seal. However, there's a lot more than I thought.
If you're on the lower body side, you can wear Mitsuhama EE suit. It's 3/3 armor so you'll really need to stack armor. It also has 5 capacity. It's pretty cheap as well. However, you can't could wear it down the street in most cases.
There's also the drysuit. It's 0/0 so you can just wear it. However I'm unsure how well drysuits work in a non-aquatic setting. I guess you could wear FFBA, then the drysuit, and then the rest of your clothes, maybe. You'll have to wear a facemask which may or may not be work depending on where you live.
*- Defined as an outfit you just wear while walking the street without being too weird or illegal
Edit- Changed my opinion on FFBA and wetsuit stacking