There are many websites that have MGBs for sale …..
here are a few:-
MGOC (see notes below)
MGCC
Car and Classic
Honest John
Classic Cars for Sale
eBay
Classic MG
Chasing Classic Cars

Some excellent advice on buying an MGB can be found here at
http://www.mgb-stuff.org.uk/buytext.htm
Condition codes as used by the MGOC
Condition of car for sale
The Club has devised the following ratings to describe the condition of MGs for sale. Members and advertisers are encouraged to use these descriptions fairly and honestly. They are in addition to the advertisement wording and are not counted as a paid word.
Condition 1
In exceptional condition, full history, able to satisfy close scrutiny in any engineer’s report and capable of winning a prize or commended rosette in a national concours d’elegance or MGOC Condition Award.
Basically as new or better than when new.
Condition 2
No faults, either properly restored or mainly original with any repairs completed to a high standard with photographic or documented evidence. Perhaps not good enough to win a respected show award but not far off.
Condition 3
Everything in good working order with minor blemishes but no unsightly areas or mechanical problems. Likely to pass an MOT in 12 months time.
Condition 4
Some rust damage evident and mechanics, body and trim in fair condition for their age. Possibly some minor work needed to pass an MOT now.
Condition 5
In need of major restoration work, possibly unroadworthy.
Value your Classic
see the Hagerty website for an idea of what your classic is worth – or what it should be insured for at