The Jonkers brothers in South Africa could also once have been described as "homebuilders" but are now very professional.
The Akafliegs (university-based gliding research departments) in Germany could also be defined as non-factory based builders but as with the Concordia project shown previously they are all going to extraordinary lengths to produce "better" gliders than are commercially available. Nothing like a kit aircraft!
Some Germans have gone to enormous lengths to recreate examples of pre-war wooden gliders (e.g. the Habicht and Reiher III) which became extinct in 1945 but that's just an offshoot of the Vintage Glider moverment.
Past attempts at homebuilts in the UK were back in the days of wooden gliders - e.g. a few T21's and Swallows were homebuilt and some "kits" exported to Australia and New Zealand to save on shipping costs.
As others have correctly said, you can pick up vintage wooden gliders for next to nothing (in some cases free) and early glass gliders (1970's ish) for a few thousand, plus the paperwork alone on a home build would be a nightmare so why bother.
The Americans have done a few kits of glass gliders in the past because their domestic glider production is very poor and I think they can use the EAA "experimental" system relatively easily.