Not aware of any regular auctions, other than Holts, Southams, Scottarms. Things occasionally turn up at the other "general" auctions - but they seldom have online catalogues, and it is practically impossible to find out about rifles amongst the other lots.

The Holts "sealed bid" normally has few Enfields, including some decent No4s from South Africa, but other than that the auction stuff is mostly scrap (if the rifle not a complete bitsa, then it generally hasn't been cleaned after proof and the barrel is rusted...) - and way overpriced because of punters failing to factor in the commission and tax....

The only way to find decent Enfields in UKicon is to scour all the remaining gun shops in your area, and also put the word around the clubs. Most dealer prices are plain silly, considering the quality of the rifles they have. The best way to "shop around" is to attend the arms fairs at Bisley, where at least you'll see 50-100 Enfields in one location (I confess that I normally have a large Enfield stand as these shows...).