All you need to do is enlist in the Marines and they will give you all the Velcro you need.lol Just kidding.
I would suggest
Marshall's Industrial Hardware just off of Miramar Rd. on Production Ave. for all your Heavy Duty Hardware Needs, this place has got it all.
Here is the link.
http://www.marshallshardware.com/
Tech Tip:
Be sure to wipe the area clean with 90% Alcohol before you stick the velcro down. Mine hasn't moved in 2 years, through fishy water and all.