Just looked at EBAY and found a ton of Beatles LP mono releases. Prices all over the place.
Mono versions of the first four albums (British version) are readily available in all formats. Rubber Soul, Revolver, Sgt. Peppers, Magical Mystery Tour, and The White Album get very pricey if they're in ideal mint/near mint condition. There were some very limited boxed set mono re-issues done in the early 80s and those often sell for $1000-$2000 per set. The individual albums are usually up in the $100 range. It might be cheaper to buy a CDR/bbotleg version of them.
I'm hoping that they will one day be released on CD or a hi-rez format (along with the stereo mixes). I'm sure it will happen...eventualy. There's too much money in it for them.