It seems that there is no service that adequately helps people to avoid the single supplement. TravelChums is not very responsive with respect to the needs of Canadians, in particular flights from Canada to places like Cuba and Mexico, and other destinations also.
Tour operators are not interested in being a match maker as there is implied liability and it seems that the resorts tend to change their rules based upon space availability, meaning the lowest class resorts are usually the only ones willing to accommodate in order to fill their rooms.
A service that would allow people to contact one another prior to departure in order to see if they are compatible prior to booking a trip may work.
If people have any thoughts on the need or design of said service, please add your post or send me a PM and we can discuss where this might lead.