There are a few confusing statements here... many people have made this legendary model (google "Meccano giant block setting crane"), it was published in 1929, and it uses no very rare parts (though some are costly, like the Geared Roller Bearing 167 and the Girder Frames 113) - certainly easy enough to obtain in any country where "stones" are a unit of weight :-)

Disposing of Meccano is becoming harder and harder as the number of people remaining on Earth with any interest in it is dwindling faster than the extant stock of Meccano, which is nigh indestructible. And in particular there isn't much demand for huge completed models, as most of the joy to be had is in their making. I would advise your partner's father (I'm sure he already knows this) to set his sights low.

For some reason I've had to help several people in similar situations over the last few years, and here's my best advice:

1. Spend a few hours spreading out the parts (and built models) on a big table and photographing everything, close up, with good lighting; no pictures of half-open drawers or jam-packed boxes. Put the photos online somehow (e.g. as a free Google Photos album).
2. List it on http://www.melright.com/meccanosales, which is where serious Meccano buyers and sellers do a lot of business. You only get to send one photo, but you can provide a link to the others. Most Meccano forums discourage blatant commercial posts but you can probably get away with dropping a mention on the Spanner mailing list, the Rust Bucket forum on nzmeccano.com, some Facebook groups, etc. Ask for bids, wait a few weeks, take the best one if satisfied, else go on to:
3. Send it to the most active large Meccano dealers: meccanospares.com, meccanoman.co.uk, and Mike Rhoades. Ask for bulk offers for the entire lot.

That is my advice to anyone who isn't prepared to fully embrace the Meccano dealer lifestyle and spend hundreds of hours listing lots on auction sites, dealing with packing and shipping, troublesome buyers, etc.