I don't think LinPlug has any U.S. Distributors or Retailers.
You could contact them directly to ask.
I wouldn't worry about using a credit card on the web since most webstores use encryption. Also, with most credit cards you are not responsible for more than $50 fraud loss (if any) if you notify them when and if you find any fraudulent charges.
Finally, you might investigate to see if your credit card provides "one off" credit card numbers. I don't know what these are called but I think some credit card companies can give you unique individual transaction numbers.