Agree with beamie. Homies has that stuff,, May not be exactly "starboard" but 1/2 & 3/8 inch 4x8 sheets of Azec type board.
I used it on a few jobs for trim, cheaper than buying separate precut pcs...
Just did a quick search on HD site here it is.. PVC
It's smooth one side - woodgrain on other
Go to stores - you should see 3/8 & 1/2 also.
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Veranda HP
3/4 in. x 48 in. x 8 ft. White Reversible PVC Trim/Sheet
•Does not require paint for protection
•Naturally resists insects and mildew
•Doesn't splinter, rot, delaminate or swell
$ 110 .00