Does anyone know of any G scale tree stumps available from any vendors out there?

Look at Landrel’s site - http://tysplanes.com/model_railroad_kits_and_parts_for_sale

Matt,

Can you sculpt with clay? If so look up a product called Magic Sculpt, it is a 2 part media that will stand up to outdoor use. A little tub goes a long way and you can make all the different stumps you want.

Chris