You don't need a 1099-B to properly report the sale of a capital asset and the associated capital gain or loss. If you look at Part II the actual Form 8949 where long term sales are reported
you can see that the only distinction between a sale reported on a 1099-B or a sale not reported on a 1099-B (your case) is that a sale not reported on a 1099-B will have "Box F" - "Long-term transactions not reported to you on Form 1099-B" checked.
In the desktop version when you start the "Stocks, Mutual Funds, Bonds, Other" interview one of the very first questions asked is "did you receive a 1099-B?" If you tell TurboTax "No" here you're shunted into a slightly different interview that the regular "1099-B" interview, but the interview elicits the exact same information:
- What was sold
- When was it sold
- Proceeds of sale
- When it was bought
- Cost basis
as you'd get off a 1099-B, and puts the sale into Part II of the Form 8949 with Box F checked.
I assume the online versions of TurboTax also can do this but because I don't use "online" TT I can't give you step by step directions.