Which federation do you compete in?
I compete(d) single ply IPF and altered my own suits many times. I can only speak to that federation. All alterations must be done on existing seams and tucks must be on the inside of the suit. For instance, if you shorten the straps, it's done at the top of the strap with the extra material on the inside rather than the outside looking like bunny ears. I took in the hips on all my suits and that must also be inside on an existing seam. I did them all by hand using a large needle, upholstery thread and a thimble to save my fingers. The advantage of doing your own is that you can make minor changes whenever you want.
The pictures are ones I posted in a t-nation thread in 2011.
Alternatively, I know of one gentleman who got his done by a local bondage shop and was happy with the quality of the work they did.