The most frequent maker whose pipes appear in this situation is David Burleigh, as he has been a professional maker for the longest time (in the current generation of makers), and has turned out the most sets of pipes.
The commonest place to find them advertised is in the Northumbrian Pipers Society newsletter, where also may sometimes be found good quality sets made by dedicated amateur, but relatively unknown makers. The editor attempts to maintain a list of pipes currently known to be for sale. Pipes are also advertised in the NSPSNA newsletter, and, in the North-East of England, in local papers. There are also occasionally sets available on the NSP mailing list, and at internet auction sites such as ebay. Some pipemakers occasionally have secondhand sets which they have taken in part exchange deals, though this is becoming less common, and most of these are notified to the NPS newsletter editor.
All of these can represent good value, but it is advisable for the novice to have their prospective purchase checked by an experienced maker or player. Repairs and restoration to a badly maintained, or just neglected, set, could cost an unwary purchaser up to half as much as purchasing a basic new set - be prepared to allow for this in any purchase negotiations.
Nearly all the used sets that come up for sale are in F
pitch, as this is by far the commonest form of Northumbrian
pipes. D chanters, and the occasional
D pitch set, are also sold. G (concert pitch)
chanters are the rarest commodity, as so few people make them,
and whole G sets are virtually nonexistent on
the used market.
Sets by previous generations of pipemakers do get offered for sale, particularly those by Bill Hedworth who died in 1994, and who made hundreds of sets over a period from about 1950-1980. These also need to be checked, as Bill's tuning and workmanship got a little erratic in his later years. Well set up, they are very nice sounding pipes.
The occasional historical find that appears, a Robert Reid set, or an antique from somebody's attic, usually goes to auction, achieves ridiculously high prices, and is frequently, and regrettably, snapped up by one of the collectors who hang sets on walls. Northumbrian smallpipes were made to make music, not adorn someone's wall.
To buy your ideal set of pipes for £100 ($150) at a car boot sale is just a pipe-dream, unfortunately. Names to look out for, however, would be Reid, Baty, Coullie, Armstrong, Hall. Many early makers did not identify their pipes, and the advice of an expert should be sought in cases of doubt.