This is one of those ideas that pop into my fevered brain from time to time and I thought I would share with those who want to roll their own . I have one out for beta testing but I can tell you it works great to hold a card scraper at 90* to a file or stone or sandpaper.
You will need 18" of 1" angle. I've used both 1/16" aluminum and 14 ga. galv. steel; both work but the steel will probably hold up better. Four shower door rollers. These are available in 5/8, 3/4/ and 7/8" diameter and are secured with machine screws (8-32 x 3/8 or 1/2 pan head). Four pop rivets or four sheet metal screws or four small nuts and bolts. Two 1" long 8-32 or 10-24 (or 32) panhead machine screws with nuts and washers. Two pieces of compression spring. I bought a 3/8 x 1.5" spring and cut it in half. All these parts are available at BORGS and real hardware stores.
Dimensions are not precise. Cut four 3/4-1" pieces of angle for the legs. Square cuts look nice, but aren't critical. Cut two 7" pieces of angle. At this stage I use a belt sander to round all the corners and deburr the edges.
Drill holes in the legs for mounting the rollers and for securing them to the main angles as pictured. Holding the main angles together, drill a hole to match your 1" machine screws through each end about 1/4" from the end and about 1/2" down from the top edge.
Assemble as pictured. The second photo shows the springs mounted to the machine screws with washers and nuts. It doesn't take much spring to hold the angles together, In use, your hand squeezes the angle and pushes down on the scraper. I found that mounting the legs on top of the main angle (1st photo) allows the legs to square themselves and only one fastener is needed.
If you want to straddle a stone, I think wider and/or taller legs.