stock control

NewBie, This is hard to explain however. I'm an Optometrist creating an invoicing and payment system. The problem is Frames have 1 item number in stock. Lenses have three item numbers. When it comes to creating an account I create a new record for each item number. I have created look up fields based on the stock number ( frames have one stock number and one item number this is easy, lenses have 1 stock number however three different item numbers to look up.) how do I create a new record for each of these item numbers. I have in the past scripted and simply did a set field type solution however the script was a mile long.

I hope this is sort of understandable

Thanks