Here's a simple Capo you can make anywhere.
Add more rubberbands or get thicker ones if it doesn't press hard enough.
If your neck has no crown (totally flat) and the thick strings keep it off the thin ones, rub it lengthwise on the strings. The wound thick strings will wear into it and it'll hold all the strings down.
If your neck has some crown (transverse curve) just whittle on the pencil til it has the shape you need.
Earl Scruggs originally used this type of capo. source: "Earl Scruggs and the 5-String Banjo"