I came across the same problem as I changed brokerages mid 2020 with the old one (Pershing NetXInvestor) providing all information, especially the cost basis of those small sales of gold buillons to cover expenses, whereas the new brokerage (Morgan Stanley) did not. In other words, after downloading the 1099 from Morgan Stanley into TT I had a number of entries to make (date acquired, cost basis, long vs short term) on each of my 6 line items.
Here is a step by step
1) Establish the lot-by-lot data (date, #shares, cost) of your holdings based on your transaction from previous tax returns or your investment tracking tool (in my case I ended up with 5 lots that had acquisition dates between 2016 and 2018.
2) Go to https://www.costbasistools.com/ and pick the calculator for the trust shares you are holding (in my case it was IUA ishares Gold Trust) and run the calculator for each lot.
3) Copy the 2020 data over into Excel (simple copy paste), i.e. the gross proceeds, cost basis and net proceeds for each of the 12 sales dates. I created a new tab for each lot, but you could also put them in one tab next to each other or below each other.
4) Do a summary calculation in Excel by adding up gross proceeds, cost basis, net proceeds across the lots (5 in my case) by sales date - you will have 12 line items.
Smell test ... my net proceeds to cover expenses were around 30% of gross proceeds, that felt about right and I was able to match the amounts on the 1099 I received from Pershing NetXInvestor for 1H2020 this way.
The one thing I am not certain about is the acquisition date I should use for each of the 12 sales entries. On the Pershing NetXInvestor 1099 they used the same date as sales date (so always a 2020 date) which is the most conservative approach I would say since there could be a mix of ST and LT dates in the underlying lots. I am more inclined to put the date of my "youngest" lot in here, which now is also in LT territory (but since these are considered collectibles, taxation occurs at a higher rate than LT capital gains anyway). Then again, this is very small money and I am not sure it matters.
