Hello.. I have long-term capital gains from a startup in the UK from 2002. There is thus no 1099-B issued by the UK company. How do I enter the gain ?

Follow these steps:

1. You will enter it in the investment income section.
2. You will choose to skip import or "type it in myself".
3. Select stock. 
4. Enter bank/brokerage - put whatever will remind you of what this is
5. continue along answering questions
6. Enter the purchase price and date along with the sales price and date.