Tyres have always been available, unless you are expecting them ready mounted. You'll just have to mount them yourself - just like we used to do in the old days.
Take your pick from these, 30 shore is very soft while 42 shore is the firmest.
http://www.rc-direct.co.uk/-c-39_198_205.html
One tyre will do one pair of buggy wheels, they are just wide enough to do a pair of rears but they are plenty wide enough to do one front and one rear.