Get your taxes done using TurboTax

I've discovered the answer, and I'm going to leave it here for future folks. It's terribly unintuitive navigation.

Note: Intuit has changed this navigation a LOT on the online version (I haven't verified for Desktop); it looks like this change occurred for the 2019 tax year version, and no help articles or navigation appear to exist for the new navigation. Where the product previously functioned using navigation like that described in this post, which indicates that you will be asked "Did you get a 1099-B or a brokerage statement for these sales," it no longer does so.

Instead, the navigation to input sales for which a 1099-B was NOT received is as follows:

1. With your return open, click the Federal Taxes tab 
   or Personal if using Home & Business
2. Then, Wages & Income
3. Select Stocks, Mutual Funds, Bonds, Other; it may appear in "Needs review," or it may be below the break under "Investment Income," depending on what actions you've taken previously within the product.
4. If you've not interacted with this section prior, select Yes when the product asks "Did you sell stocks, mutual funds, bonds, or other investments in 2020?"
5. If you've interacted with this section prior, select Add more sales, or select Review on an existing sale if you had one created but were struggling to find the option for no 1099-B. 
6. If you selected Review, just follow along with the below until this navigation reaches the page that it dumps you out on.
7. If you selected "Add more sales," select "Stocks, Bonds, Mutual Funds" and hit Continue.
8. On "Get ready to be impressed," select Continue
9. On the resulting page, select I'll type it in myself.
10. On "Which bank or brokerage sent you a 1099-B for these sales?," simply select Continue, leaving the fields blank, since you did not receive a 1099-B.
11. On "Tell us about your 1099-B sales for this brokerage account," answer the questions asked as they pertain to the sales, despite your non-receipt of any 1099-B at all, then select Continue.
12. You have the option here to either select I'll enter sales totals instead, or to enter sales one by one (represented by Continue). Pick either option, though it's likely wiser to enter them individually if you have more than one, since the IRS will not have received a Form 1099-B for these either.
13. Select Continue on the resulting page, which simply reminds you to go get the 1099-B you don't have.
14. On the resulting page, under the "Sales Selection" drop-down, select the appropriate option - which should be either "Short-term basis did not receive a 1099-B form" or "Long-term basis did not receive a 1099-B form." You will need to consult your own documentation for whether your sales are long term or short term.
15. Input the sales information, and go on with your life, content in the fact that you've triumphed over Intuit's questionable product navigation.

I'm going to leave my customer feedback on this issue here; this wasted multiple hours of my life. I hunted high and low before just navigating my way through everything to find this answer. I thoroughly dislike Intuit's product design team right now for their choices which lead to this navigation configuration.

It's unreasonable to expect users of your product to somehow know that, at the very end of a navigation chain that constantly reinforces that it is for "inputting information received on a 1099-B," there will be an option indicating that no, a 1099-B was not in fact received. This is further reinforced by the inclusion of several "optional" fields like "Payer EIN" in tandem with fields NOT marked optional like "Payer Name." Traditionally, if you show optional fields, then the remainder are mandatory fields, and this is a big flashing red light that says "hey, if you didn't receive a 1099-B, this isn't the right navigation for it!"