An RV place might be able to do it but I doubt that they have had any experience in such repairs. There was a good post which specified the type and size of bolts and nuts needed for the X braces on this forum within the past couple of months (it sounds like you might have read it already). I'd suggest first getting the bolts and nuts you need (note the "grade" suggested since you want bolts which are stronger than the original ones) and get them yourself from a hardware store. I won't go to Home Depot or even Orchard Supply Hardware for them since they don't have the most knowledgeable staff. It sounds like you are across the bay from us and I'd suggest Dale Hardware in Fremont...unbelievably well-trained staff. You might call them first and see if they have them in stock and, if not, if they can order them for you. The other option is to order them online. I don't recall if that post indicated where that owner got his but, if not, try McMaster-Carr (www.mcmaster.com
)...I'd just call them rather than try to find them yourself on their website.
Next, I'd suggest putting up the top and measuring the distance between the inside of the roof and the "ledge" in each corner. Whoever replaces the bolts will need to put up the top and prop it up so that it won't come down when the bolts are removed and replaced. With those dimensions, go to a lumber store (again, not Home Depot) and buy some 2x2 lumber...have them cut them to length. They will charge you a few bucks to cut them to length.
A couple of ideas about getting the bolts replaced once you have the replacement bolts and nuts and the lumber to hold up the top. One, you might check Yelp for a handyman (the kind who advertise, "No job too large or too small").
The other option is to call Towne Ford in Redwood City and ask to talk to the Service Manager. Jay Minto is the fleet manager at Towne Ford and they supply all of the Fords to Sportsmobile. The Service Manager should therefore be familiar with the SMB penthouse. Ask if they could replace the bolts if you have all of the items needed to do it. I'm guessing that it would take an hour or so of time. If they can do it, stay there so that you can answer any questions and take a printout of the forum response mentioned above. I'd also get a small "blue tarp" (from Home Depot) to put on the floor of the van to protect it from tracked oil, grease, etc. Make sure that the mechanic can easily get to the four corners of the van to put the 2x2 supports in place once the top is up.