Yes, there is a way!
- Click on the Watch button on main menu.
- Click on the Your Matches button.
- Pick a match from the left-hand side of screen, and hit the "Copy Share Link" button on right top.
It'll copy the match link to your clipboard, which looks like this:
Which you can send to your friend (through steam or other platforms, but some browsers might block that link).
Your friend will be able to download the demo as long as it is stored on CS:GO servers, which is about a week.
If the "Copy Share Link" button doesn't have a download button on its left, your friend will not be able to download it and will receive an error similar to this: