Maurice,
I made a few phone calls today and am no further on about the Quay in Donegal Town but Ive got some other good news.
Take the road out of Donegal Town towards Mountcharles/Killybegs for about 3-4 miles and look out for a sign SALTHILL BEECH on the left hand side of the road before you come to Mountcharlesthis is helpful and that you have a super time in Donegal.
Go down that road towards Donegal Bay and there are lots of place along the sea front where you can park without any problems.
Hope you have a super time in Donegal.