I donn't know of any sit that has boattraikers but if you are interested in building one, go to a mariena and get the mesurements from one of their trailers that will fit your boat or possably a friend who has one. Take a ruler, protractor for angles messure thickness, hight and width of material and draw a detailed account of every piece. With the info you get you should be able to put together a trailer without much problems.
ColdFeet