I'm in zone 7 b in North Carolina. The best agastache varieties in my garden (that were stellar during 90+ days with 90-100 degrees and little rain or supplemental water):

Cotton Candy (blooms mid-April until frost)
Salmon & Pink
Blue Fortune

I have many varieties, but those are my top 3 favorites for length of bloom time, heat resistance and surviving our winters.

My garden has FULL SUN, ALL DAY--from sunrise to sunset!

The only variety that hasn't done well in full sun, but survives anyway, is Golden Jubilee. The golden leaves get terribly scorched. It looks great at the beginning of summer, then a bit ratty due to the burn.

I grow my agastache with salvia greggii, nemorosa, and guaranitica varieties.

Cameron

Here is a link that might be useful: my agastache photos in August 2010

You might try aurantiaca and its hybrids and rupestris. Neomexicana might be another that would work. My own experience might not be all that applicable to you since our hot isn't exactly the same as yours although we complain just as loudly. Here the winter is our concern, keeping the crowns dry enough so the don't die in late winter early spring. If you can get hold of seeds you could try growing out a big batch and then see which seedlings can take your weather. Once you know that it would be a simple matter of cuttings. It is pretty easy to start from seed in trays and then transplant the seedlings to cells. It takes quite a while for the new seedlings to get to any size. This year's batch is just reaching a size where they can come out of their cells and into the ground - they were started New Year's Day. These seedlings will bloom the first year but won't get to full size until year two. Would that mean in your climate you'd start them in fall? There are other Agastaches - need to think.