Go on their website and checkout as you normally would but select money order as your form of payment. Print out the invoice and mail it in with your MO. I got a shipping notification a day after it was delivered to HKParts.
Talked to them last Thursday or Friday, Liz told me the credit card thing is taking much longer than expected. They are fixing the orginal problem and upgrading their credit card payment system.
In the meantime I've put items in my basket, checked off the box pay by money order and mailed a money order down in a $6 #10 Priority Mail envelope and got my parts in 8-9 days including the mail time from Alaska.
George from Alaska
HK45T Light LEM
Mark 23 90's era, no lockout
P30L v3, another on it's way
P30L Light LEM
USP .45 Elite
registered MP5 SEF select fire
other NFA items
Got the order promptly after sending the Money Order...
Received my order a few days ago. Whole MO process took a little over a week.