I know that Eduard has a set of tie down straps in photoetch, but does anyone make just the buckles, as I would prefer to use paper, etc instead of a complete photoetch strap.

Verlinden does a set of buckles that come with a piece of lead foil to cut your own straps. But you could easily use paper instead. There were a variety of buckles to use for rifle straps or tie downs, etc. It is set #0433.

There was a post here not too long ago about making buckles for straps on figures using miliput or other epoxy putty. I think it was linked out to figureplanet.com. Here's the link...
http://www.planetfigure.com/articles/buckle.php

Another alternative would be to cut a buckle from lead or aluminum foil and slip the strap through it before placing the strap. Otherwise, cut the middle part of the strap and simply slide it under the strap to complete the effect.

Historex plastic 54mm Napolionic figures always have a few extra buckles with just the strap ends molded on. The mounted figures have a sprue with lots of these buckles, in two sizes, I think. Of course, you have to buy the whole figure. Hope you like Napoleonics too!

I usually do them using brass or copper wire...
Ciao