Oh and I almost forgot - Chapman has several drawings in his Navalis Mercatoria - also available from Amazon.
With respect to actual plan sets, unless the design is modern or re-drawn the drawings in Chapman, May and Chappelle - coupled with a firm knowledge of boatbuilding techniques - may be your only recourse. And the former almost never yields historically accurate designs, favoring simplified construction and improved longevity instead.
Let me know if I can help in any way.
WRK