You must be thinking of the first and second Doctor's eras, quite a few of their episodes were "wiped" by the BBC in the 70s (when they switched to color and wrongly assumed nobody would watch the old B&W episodes anymore)
Pertwee's era is completely intact and EVERY episode has been released to DVD by now. About 3-4 of the serials were missing the original color broadcast and were only available in B&W until recently, but the BBC either restored the color negatives or colorized the missing ones for the DVD releases.
Since it looks like I'll be boycotting season 10 of nuWho (shame, Capadi was an interesting choice to succeed Matt Smith), now is probably a good time for me to start watching all the episodes of the Pertwee era. Doctor Who had class back then.
In England, perhaps, but not available on iTunes; however; some are available as US playable DVDs (but not all) from Amazon; most Pertwee episodes are extremely hard to find.
With the loss of Jenna, a beauty, and the addition of Bill, and ugly lesbian crow (the ugliest companion ever - and perhaps the only one who is ugly), Who has gone so far downhill, it has become unwatchable; Capadi addition helped the slide into oblivion.
Bill is one of those people that once seen can never be unseen ...