Don't think there is one Ron. Certainly there has been a growing polarisation of major tackle buys towards a relatively few mailorder companies.
Talking specifically about maggots I tend only to buy them in the winter when targetting grayling. From a quick mental review more alternate baits spring up and are"refined" each year. I can foresee the day when traditional livebaits such as maggots and worms are only available from either large fishing stores or on site at commercial fisheries.This seems to appeal to certain sections of the sport who, in common with large parts of the general public, expect everything done for them.You know the scenario, turn up. buy bait, catch a sackfull of starving fish and in the pub to watch the match.
I certainly think that conventional, small tackle shops are on the way out much in the same way that the corner shop, the butcher etc have demised. The blame lies with us for not spending enough, society's desire for instant low input gratification - just look at the parlous state of club memberships, the ease of mail order shopping via credit card. End of rant.