If you want a new bimini and are based on the south coast then C&J in Chichester do all the canvas work for Bavarias. They will have a photo of the fitted article for a 38, I expect, and can give you a quote including fitting. I have used them for sailcover, sprayhood and cockpit tent with good results. They are probably not the cheapest but after sales are good and they will fix any niggles you have when the product is fitted.
That said, there are many other suppliers of canvas work around the country, many of whom could make one to your design.
Second hand biminis are probably in short supply. I would imagine folk tend to hang onto them, once fitted, like they do with a sprayhood.