Try this:
Open Finder, on the top menu bar of the screen, click on "Go" and then "Go to folder..." to open a dialog box. In that dialog box type "~/Library" and press Return. Finder should open your LIbrary folder. In that you should see a folder for Mail. If you can't find it, open the Finder/Go/Go to Folder and enter "~/Library/Mail" and if it's there at all, it should open in Finder. What is there is kind of cryptic, as it's not intended for the casual user to mess with.
EDIT: Once you get to the Mail folder, open TM while Finder is there and the "Finder-like" presentation in TM will be in the same place. But remember, as I said, what is in that area is cryptic and the names are not what you would expect. For example, there may be a folder named "V10" with randomly named folder inside that. Here is my Mail folder, as an example:
View attachment 39569
Each of those subfolders of V10 have more folder nested in them, and they have even lower folders nexted in them. For example, I separate the email messages I get from this website into a separate folder in Mail, so I have this:
View attachment 39570
The actual messages are the ".emix" files, but any attachments to those messages are stored elsewhere, in a folder calle MailData. The naming of the emix files is sequential, as far as I can see, with the messages then stored in the 0, 1, 2, 3 folder and then in other numbered folders. All of that is to say that finding an actual single message to restore is going to take a lot of searching.