Where to find flush mounted deck access plates?

[Lars Koster]

I have a 76 Sceptre and was trying to find the round 8" deck access plates that would fit exactly to the boat. I purchased a few different types that did not fit in the recessed lip molded into the fiberglass. There are 4 total: 2 on the deck in front of the splash well and 2 vertical to access the aft corners.
Any help or comments would be appreciated.