How do I find another member of my level who is looking for a partner?

In Partnership Desk ( after entered the tournament site ) you will see the profile of ONLINE members who are looking for a partner, and there you can see their skill level in their profile when holding the mouse pointer at a specific name

As substitute, my score in the tournament was not very good, because I was given the score of the person i replaced, mixed with my own score.  Can this be adjusted?

No. As a sub you get the score of the player you take over for, and build on that.

But look also into our rules for RANKING ( Tournament points ) ( You see link to the complete left )