Your'e in luck, folks. It is indeed "The Strathallan Early Music Group". I know this because it was my brother who made the tapes, and I'm sitting looking at 2 of them right now. You made mention of "O'er Hills, O'er Mountains", which was recorded in 1988. I also have "The Beggar's Meal Poke" which was recorded a year earlier on Dougie MacLean's "Dunkeld" label. The brains behind these projects, as I recall was a guitar player called Jo Lozowy, who I met years ago, but haven't seen in maybe 15 years.
I don't know if these recordings ever made it onto CD - I'll ask my brother next time I speak to him, as he would probably have made the CDs as well.
Alternatively, there is an address on the "O'er Hills..." tape which you could write to and ask. The address is :

"Terpsichore Music",
4 Campbell Street, Coupar Angus,
Perthshire PH13 9BW

If you write to them, and the recordings are no longer available either on CD or tape, ask them if it would be OK for me to "Digitise" them onto a CD for you, and I'll do that.
It may help if you say that the person making the offer is the brother of the guy who made the recordings for him in the first place. I'm not sure if Jo would remember me or not - it was a good while ago we met.
Good luck,   Kenny