The plural of boar is
boar.
Sounder is not archaic in certain circles.
Singular is, I believe, archaic, but it didn't refer to a group - it refers to the solitary way of life of certain adults. The reason these terms are unfamiliar to English speakers is that boar are extinct in the British Isles (Anerica?)
On teh continent of Europe, they're so common that in France they're no longer classified as game, with a closed season and a resyrictioon on who ccan shoot them and how many, but as vermin, which can be shot at any time by anyone with a huinting licence. In France in 2008, of 42,471 declared road traffic accidents cause dby wild animals, 16,797 were due to wild boar. There are - forgotten the name in English - when a group of hunters surround an area, dogs are sent in and the game come charging out (or leaping if they're rabbits or deer.) Hundreds of thousands are shot each year in France, Germany, Romania.. I could supply dozens of links in French, but here's one in English
http://www.spiegel.de/international/zeitgeist/0,1518,663411,00.html
If I speak to my hunter friend in England, I'll ask him about English boar-hunting words in use. Hunting (hunting with dogs, but on foot) shooting (also with dogs, but dofferent breeds) and falconry) are vastly popular in France, Spain and many other European countries.
Special words and expressions are used in most field sports and in most, as in archery, fencing, cocking and other long-established and still traditional sports, many of the terms haven't changed for centuries. The fact that they aren't generally known isn't a reason not to use them.