Yes the offer on the market is appalling, from this point of view. One phone I know that was supposedly designed for elderly users, the Sagem VS1, still falls short of the mark _especially_ as button size is concerned.
Nokia has a page called www.nokiaaccessibility.com which claims to address special-needs users, but both the page and most of the phones being offered seem to have been designed by teenage droids who never had a parent or a grandparent.
I suggest having a look (note: I am not recommending them because I don't know them; I just suggest it may be worth checking) - at one of the "fixed mobile" phones, i.e. ones that use the mobile network but are meant for use in the home. One such phone is the Sagem myH 10L.
Another product you may find interesting is a device (not sure what it is called) that connects wirelessly to the mobile network and has a socket into which you can plug an ordinary fixed-line phone of your choice.
If you have the patience and the nerve, you will do all of us a favour by calling various mobile phone operators and sales outlets with your questions. Eventually, the message will filter up their chain of command and bear fruit.
Good luck, you'll need a lot of it.
Leszek.