Generate list of encrypted codes

Say I have four surnames each sporting a unique 3-digit code:
E.g. Smith = 411, Jones = 412, Doe = 413, West = 414

For each surname/number pair, I'd like to generate a list of say 200 unique 10-item codes, that are then encrypted so as to mask which surname/number pair was used to create each code. I thought each 10-item code could comprise:
Item 1-2 = first two letters of the surname
Item 3-7 = some random number, possiby generated using the system clock as seed
Item 8-10 = the 3 digit code.

As I say, these 10-item codes are then encrypted in such a manner that when the complete list of 800 (4 * 200) codes is generated there are no duplicates, yet each can be decrypted to reveal which surname/number pair help seed the code.

That make sense?

Any advice/pointers/code snippets that will help me achieve this in VB.net (visual basic) would be greatly appreciated.

Thanks in advance.