Well, there is certainly no problem finding alpines hardy to zone 5!
The attached plant list suggests zone ratings for a terrific selecton of alpines, if that's what you're looking for. (NB> I am not experienced enough with alpines to judge if the zone ratings are reasonably accurate or not, but it's a start.)
Lori

PS Sorry your post has gone unanswered for so long. The reason I personally have hesitated is that it's unclear if you are looking for true alpines, or plants that require enhanced drainage, or simply for lower-growing perennials with which to replace the taller ones. (My personal definition of "alpines" is high montane plants that really require enhanced drainage, and won't do well in regular garden soils - though often the definition is much looser.) I sort of sense that it is the latter, but if not, enjoy the list - I find it quite useful.

Here is a link that might be useful: Beaver Creek alpines list

The salt spray in winter is what's had me wondering about what might work. Then I remembered reading something about aplines/rock gardens by the seashore on alpine-L this year. The link is below to a posting that listed several plants that can tolerate salt spray. I'm not sure how they would do in your climate though. I would also add delosperma cooperii and silene uniflora 'compacta' to the list of plants that may work for you in this area.
Some plants that I've seen growing on rocks are Petrophytum caespitosum and sempervivum arachnoidea/um (sp?).

Here is a link that might be useful: Link to alpine-L post

Hi. I just checked this post again and there were responses! Thanks. I will check those out. By Alpine I meant low growing plants that will enhance the beauty of the rock, not cover it. I believe technically I may be Zone 5b (southern Ontario).

I saw carpet roses listed in a magazine the other day that they were saying were low growing...wonder if they would work?

Where is there salt spray in southern Ontario? I always thought the Great Lakes were fresh water, and Hudson Bay ain't south. :)

Rosie stated that this planting area was near the road and would suffer from "salt spray" from I assume snow plows/road graders during the winter.
I don't have this particular problem, so I'm not sure just how much of an issue the salting of the roads and subsequent splashing of it onto plantings may be.

Roses aren't really salt tolerant with the exception of Rugosas, I doubt you'd want a monster like that hovering over your rock!

Iberis sempervirens, Candytuft, and Armeria maritima, Sea Thrift are salt tolerant and would complement your rock. Veronicas are salt tolerant and several, such as Georgia Blue, are short growing creepers. You'd have to check and see what would grow in your zone. Thymes don't make much in the way of flowers but they're salt tolerant, fragrant, and come in a variety of colors, textures and variegation.

Portulaca grandiflora, Moss Rose, is an annual but it might also suit your needs.

Missed the mention of it being from the road! That explains it. Maybe because I live on the coast and think of "salt spray" as being from waves, my mind did a cognitive dissonance thing. :)

I'd agree with delosperma - as Sagebrushred already suggested, and also perhaps a dwarf soldago (goldenrod). You may want to research a bit about plants that naturally grow in crevices on the coast of Nova Scotia, PEI and other areas that get salt spray year round. Many such species are good alpine substitutes.