The most important thing is to get to the correct brace height. My Bob Lee chart says your bow should be braced at 7 5/8 - 7 3/4". Whatever string length it takes to get to that brace height is what you should use. You can, of course, fine tune it from there.
If that turns out to be a 56.5" string, and you can get someone to build it for you, then that's what you should do. If not, then I would order a 56" string and let it stretch in use.
There are many fine stringmakers on this forum. I almost hate to mention any, because they are all so good. But Chad Weaver, Ten Ring Strings, and SBD Bow Strings come to mind. I'm sure there are others that are just as good that I'm not familiar with.