It's usually the loop side that gives out long before the hook side.

You can buy velcro in various widths from a fabric store. Usually you have to buy both sides, occasionally they'll sell the hook part and loop part separately.

My shoes aren't there yet, but it seems like it wouldn't be that big of a deal for a cobbler to replace the velcro. I might even make a stab at hand sewing it myself using the existing needle holes (probably best anyway so as not to weaken the strap).