"There is also evidence that big builders acquire large plots of land in a local area, then put up houses deliberately slowly in order to maintain the local market price."
A common cure to this type of behavior is competition, so this tends to happen where there isn't competition. Maybe a developer owns too much of the land in an area, or maybe it relates to a local rules and preferential treatment via corruption or other effect.
I don't put much stock in the idea that developers are getting together to rig the system though. Multi-party, secret agreements like that, where one whistleblower can bring the whole thing down are uncommon. The typical corruption system of powerful "brokers" is a more common arrangement.
A solution to the lack of competition when it occurs would be public auction of developer land, as eminent domain, if targets aren't met.
As an example, the rule could work like this: Say one developer owns all land in the area. If they don't manage to complete and sell x number of homes (based on some industry average), then some portion of their undeveloped land would be put up for auction. If there are any buyers, now you have a new source of competition.