vee-tail-1,
The gliders operating in the immediate vicinity of Talgarth listen out on 130.1 MHz, which is one of the four frequencies allocated to gliding. You're very welcome to communicate your position and intention on 130.1 MHz when passing Talgarth airfield. The air ambulance helicopter does so routinely, and his courtesy is appreciated. You will most likely not get a response from Talgarth airfield, as the airfield does not employ a FISO and is not licensed to provide a flight information service. I would hope that any glider pilots who are close to your intended track would pass on their own positions.
If you're concerned about flying in areas where gliders are likely to be operating, I recommend that you purchase a PowerFLARM unit. This will give you situational awareness of any gliders and other aircraft operating FLARM.
I agree with you that a low cost (and therefore likely to be uncertified), low power device to provide electronic conspicuity and collision avoidance for all Class G airspace users, from commercial airliners to microlights, gliders, paragliders and unmanned air vehicles, would be of great benefit to the flying community. At the moment, we have a plethora of technical solutions (transponders, ADS-B, TCAS, FLARM and now TABS), each of which only meets the needs of a subset of Class G airspace users.