Yellow corydalis, which is the common every-day one, so it should not be hard to find. I get all of mine by mail order with no trouble. It makes a lovely ferny mound, and the little flowers are bright yellow and stand out well in the shade. The foliage is a soft grey-green. Related to bleeding heart. You will have to check to see if you have to treat it as an annual in your zone, but then the impatiens would be an annual for you also...

Jackie

There are yellow African Orchids which grow well in shade.

Melampodium does well in sun or shade.

tj

There are begonias in that color. And try some coleus in those colors also. I think it would be a pretty area with those colors.

Depending on the space, you could also use ligularia

I thought I was seeing things... or having a senior moment!

Here is a link that might be useful: similar discussion you might like

Leopards Bane might work too....although I don't think they're hardy to zone 2