Save the "heels" (or "end pieces") from your gluten-free bread to make your own breadcrumbs, and store in your freezer in a freezer-safe container/zip bag until you have enough bread to make your breadcrumbs.
When ready to make breadcrumbs, defrost bread heels and cut into cubes. Place on a baking sheet and toast in 300 degree oven for about 25-30 minutes or until lightly toasted.
Allow to bread cubes to cool and dry out completely on the baking sheet.
Transfer to a food processor and whizz to the desired breadcrumb consistency. Store in your freezer.