http://bowrivercanada.com/hatch-charts/
Here's a hatch chart of the RDR to get you started. It doesn't contain early May but there should be black winter stones and bwos out I believe.
As far as not knowing what to ask for in a fly shop, the best advice I can give is just go there and tell them you're new and want to learn new flies, ideas etc. They will know what is working best as they are always on the water and talking to others who have been. Don't be shy, we all started at the bottom at one point.