This is easier than you think, what you will need is:
18" of cotton or jute cord
1 heavy bead, washer, jewelry finding, or a button
The object that makes your pendulum base needs to be heavy
enough to keep the cord slightly taut.
Attach the selected object to the cording by tying, looping or
stringing. Your can either have a single cord at 8-10 inches, or a
doubled string using the entire 18 inches of cord.
Cotton cord or jute seems to conduct the best flow of current due to
the natural fibers, but the choice is yours. I've seen pendulums on
chains, fishing line, or plastic cord.
Making your own pendulum gives you a connection, and it's easy.
Here's a photo of a few as an example, description below the photo.
From left to right: Glass bead with caps strung on a single cord. A jewelry finding
strung on a double cord. A stone with a hole drilled through it, with a decorative
bead and a single cord. An old shank button with a decorative bead on a single
cord. A steel washer looped on a doubling of cord.