There you go
Well, since that one doesn't include the pins, it's not going to help him very much.
You can get one from a Hobie dealer (use the dealer finder at the top of the page) or from Murray's (http://www.murrays.com
). Murray's sells a "heavy duty" version (http://www.murrays.com/01-3021.html
) that resembles the very first step links used. The current versions (like the one in the eBay link) are meant to be permanently installed, whereas the Murray's one is meant to be removed after use.
To convert a '70s "hook" mast base, you cut/file off the hook (just the hook, leaving a nub like a new mast base), drill a 7/32" hole through the middle of the nub, drill out the rivet in the mast step and you're done.