The one thing that people like about our shop is that we make anything they want. If we just buy items and resell them. It makes the items less custom or less valuable . Anyone can resell someone else's work .
paper-inserts for an exterior sign? seems chintzy....
seems easy enough to do in-house, however, but I've never seen it as an "off the shelf" item from any supplier.
edited to add: both pics appear to be simple extrusions, cut to size & bolted/screwed/rivot'd on, with a piece of acrylic/polycarb that's thicker on top/bottom than in the center by adding a strip of <1/8" material.
if it were me needing to make this for a client on the fly, maybe design it around the standard cut sizes of Avery peel&stick material that comes off the shelf at local walmart/officesupply. client can print a sticker for their special instances, and slap it on. won't fog-up with humidity, or fill up with debris over time.