Does anyone know of a website where I can find short-term (stop gap) carers?

[itsanewday]

My mum is about to turn 73. She is fit and healthy but totally worn out. She is constantly trying to organise live-in care for her own mum, who is 98 and still living in her own home. She has had live-in carers for several years now. She is frail, and her hearing is not good, but otherwise she is all there. My poor mum just really struggles to keep her cared for. The big sticking point is that they are (both) in the rural highlands of Scotland. The carers need to come from Scotland, to reduce costs but also travel stress due to weather etc. They had a great system of two carers, two weeks on and two weeks off, alternately, but then one wanted to change to 10 days on two weeks off, which meant that they needed some-one for four days. Basically, it is in a constant state of flux. People can do bits and pieces but it doesn't necessarily jigsaw together; people let her down all the time, not always through their own faults.
Gumtree just isn't coming up with the people, and needs to be paid for now - and agencies are so very expensive, which is fine if it's a one-off but this is constant. One person that is coming at the moment, but is short-term, has said that there are always people looking for care work to fill time off etc but we don't know how to tap into these people. I do know there are whole communities out there, online, which you don't really find out about unless you have reason to get involved. Does anyone know? She's really tried everything and she is at her wits' end and waking up every night worrying about it. My Gran now needs wraparound care too as she needs help to go to the bathroom in the night. She can't be moved as she is too old, and doesn't want to be...