'official files from Nokia' ????

what on earth are you talking about?
Nokia catalogs never contained anything for xterm.

There are only a handful of somewhat requisite files from Nokia.
everything you need should be in 770 maemo extras repos....and 3rd party repos.

the most extensive list of maemo extra catalogs and 3rd party catalogs are where you have already been...
Gronmayer's....
THAT is where you will find the most comprehensive 770 catalog list there is.

I am sure the Nokia cats are listed there for the 770....but you don't need them for this...as well.....they are offline and have been for years....and years...there are places such as the wayback machine that will have the Nokia cats...but they aren't your immediate priority here...

check the cats at Gronmayer...the official maemo extras cats should also be listed there ...make sure any cats you choose are online and contain files...before adding them to your App Man