Welcome. I lived in Milton, twice, my wife is originally from there... Classic Mustang specialists? Few and far between... All parts for these car.’a will generally come out of the USA. You don’t mention exactly what you are searching for; mechanical, paint and body help?
Word of mouth is usually a good start in searching for the right help. Talk to other classic car owners in the area to see who they use. Check Kijji, place add’s and review the feedback you get from people. You need a mechanic that understands how to work on the old car’s, getting harder to find today as they retire. Of course, the more you can do yourself the better. As for the missing shock tower brace, I would look for a replacement as there is a reason why the factory installed them on these car’s originally. Seeing that you have a vert, becomes more important. However, you can still drive it but I would look for the missing piece ASAP. Someone here might have it and can send to you. Also, members here like to see pics of a new member’s car.... BTW, I am in Welland now, I have two verts (71 and 73) and a 73 Coupe.