You don't want to join one of those.
I did my first Munro in 1990 and in my experience organised hillwalking clubs are predominantly male, bearded, middle class, aged 55+ and invariably patronising and BORING!!!
You can occasionally come across them in SYHA hostels, gently dozing away the long evenings while idly thumbing through 5 year old copies of TGO.
In my experience 99.99% of walkers you meet on Scottish hills are either alone or with people who are obviously good friends or family. In seventeen years of wandering the Scottish hills I have come across organised groups actually on a hill just twice.
Read Muriel Gray's comments on organised groups in her book Munrobagging without a beard, no words were ever truer said.
If you want to find people to go walking with, if you are lucky enough to have a good outdoor shop locally try an ad on their notice board. You could also try various net forums. Walking Britain is quite friendly. The Ramblers are a bunch of boring old farts but they have a very well patronised forum and a lot of people use it who would never go on an organised RA walk.