Perhaps go to eBay
and find another Ajax album (or just the binder), then find some blank pages (or an adequate substitute size-wise and appearance-wise). Or, buy similar paper stock, print a similar type of border/header/descriptions, punch holes in the right places and add them to the old album.
If it were me? I'd revel in the idea of getting a larger album and HAVING to transfer from old to new. But I am weird (aka: stamp collector) that way. Another search on eBay
should provide a long list of used albums - find another of the desired vintage, but larger than the one he now has, and transfer into the larger album. It's kind of like the Mrs is pregnant AGAIN, and although you are happy with your current house, you HAVE to buy a larger one to handle the new stamps... er, kid.
Your father's options may be limited.