Where can you buy Dr Wilkomm Riesling wine in the US?

I was able to purchase Dr. Willkomm's Riesling at Sam's Club in Fresno, CA about 6 months ago and haven't been able to find more. That's why I posted the question also. I have found other riesling at Sam's but it is not the same taste by far.

I have the bottle in my hand and there is a website of www.BlueRiverRiesling.com for a contact. It's imported by Blue River Imports of Princeton, MN.