Denver asian supplies
I don't know Denver, but in Boulder you can get them at either the Indian market or Asian market at 28th and Valmont, and I believe the Indian market at Table Mesa and Broadway also carries them. Pacific Ocean Seafood Market in Broomfield would almost certainly have them as well. And I think Whole Foods in Boulder has them sometimes, so you might try asking at your local WF as well.
Not too sure about curry leaves... but there are for sure several spots to get kaffir lime leaves. I moved to Denver in November, and I cook a lot of Thai food (curry paste from scratch, soups, etc) so I spent a whole day browsing the Asian markets in Denver so I knew where I could get what I needed... here's my results:
Ocean Pacific Market (on Alameda between I-25 and Federal), Little Saigon (375 S. Federal) and New Saigon (1076 S. Federal) are all Vietnamese markets. They all had fresh kaffir lime leaves. They are heavily slanted towards Southeast Asian products and produce. The selection was mostly the same at each... some having better produce quality than others, but overall good choices.
HMart in Aurora (on Parker Rd.) is a Korean market that has a great produce selection and also lots more Chinese and Korean products... don't expect to find kaffir lime leaves here... when I asked if they carry them, I mostly got blank stares.
Pacific Mercantile (downtown I think on Lawrence) is a great Japanese market. They carry a good selection of other products as well... they don't have a huge produce department, and I honestly can't remember about the kaffir lime leaves, but otherwise it's still worth checking out.
Lek's Market (172 Del Mar Circle in Aurora- closer to I-225) is a small, but great Thai Market. The lady who runs it is great, but they don't carry any fresh produce. In a pinch she does carry frozen kaffir lime leaves and whole frozen kaffir limes.
Hope this helps... happy shopping... and eating!