TurboTax Business does not support PDF attachments for e-filed returns at this time. You can still e-file your return, but you'll need to mail a paper copy of your 1099-B to the IRS along with Form 8453, which you can print using Forms Mode.
Mail these completed forms to the IRS at the address below by the tax-filing deadline:
Internal Revenue Service
Attn: Shipping and Receiving, 0254
Receipt and Control Branch
Austin, TX 73344-0254