Not sure how long ago "BillQuay" is talking about, but I'm afraid there are no boats to hire for fishing in Brodick Bay anymore and as for Cod and 10lb Ling...............................................well??
Lamlash is not only a no take zone, it is a no fishing zone, so be aware.
Rock fishing - well there are some flat red rocks at the far end of Whiting Bay, a small stone jetty at Corrie and rock marks at Blackwaterfoot. Maybe worth a go, if you don't mind poor returns.
You will not find bait in any shop, so take spinners, jellies etc and hope for some fresh Mackerel.
Arran is a wonderful Island, especially if the weather is good and I am sure you will love it, but don't expect too much on the fishing front.