Brass/plastic part to keep toilet seat lid from lying back too far
I have tried all kinds of search terms with no luck.
I would suggest that you affix something  to the tank that the seat will rest against instead of the flush handle. It would need to be thick enough to stop the seat before it reaches the handle (and not so thick that the seat will not stay up)
Perhaps a nice piece of foam wrapped in some material that matches your decor or towels.
You could use some light duty hook and loop fastener (Velcro) on it and the tank to affix it so you could remove it form washing it and cleaning the toilet.
If it proves to be successful then we can advertise it with late night TV infomercials and make millions.

(Actually we could do that regardless of whether it works or is even necessary and still make millions as long as we speak loudly and with conviction)

OR You could even just place something on top of the tank thick enough to stop the seat before it reaches the handle (and not so thick that the seat will not stay up) like a decorative box to hold potpourri or scented matches or grandma's toilet paper cozy.