Want to find the money? Increase the ability of the IRS to perform more audits. The richest folks are already not paying the taxes they should be. $688 billion per year!
Yes, but Moscow Mitch serves the richest elite who have rewarded him handsomely over his career. So he can't allow them to be audited or taxed if he can help it.
The Senate is also proposing spending bills. It is up to the House to ratify it, but that doesn't mean the Senate can't make their own contributions. Schumer has announced that the Senate will vote on some budget bills today, and McConnell is indicating his support depends on their willingness to further engorge the deficit so his wealthy patrons can benefit.
McConnell is not trying to tie Ukraine/Israel military aid to IRS funding. He is trying to tie military aid to increased funding for border security. And he might well succeed, especially as cities like Chicago are starting to complain about immigration.