You know a reef store is serious when the name has been shortened.
Ocean by Design as per post #2. They do keep regular hours but calling ahead is often a good idea. The uniseal is on the shelf next to the counter. I think they have 3/4" and 1" on that shelf.
I used the 1" for a top penetration into a sump (no fear of leaks) but the 1/2" acrylic is too thick for the 1.75" hole so be sure to check the spec sheet.