Something like this?
https://imall.com/product/Motherboard-164P-PCI-E-socket-connector-16X-Graphics-card-slot-fishtail-PC-DIY-PCIE-164-Pins/Lights-Lighting-Accessories-Connectors/aliexpress.com/33007839512/568-682140/en
Could you maybe draw picture of what the end result you are looking for is like? The common storage way is to use original boxes and/or anti-static pouches + some box. This is how I've stored my extra cards.
You can DIY pretty much anything for very small budget, depending what the end result should be like. For example are you looking to display extra cards on shelf or just storing them. For storing only I would use soft cellfoam or cardboard to make base with slots holding cards. Put them into anti-static pouches and you have then available and secured from dust etc.
Or you could get something like this https://www.aliexpress.com/item/4001170039274.html?spm=a2g0o.productlist.0.0.246c3061Zpup3j&algo_pvid=9a52bd52-ab8a-4523-abaa-0f0d6fbf9e37&algo_expid=9a52bd52-ab8a-4523-abaa-0f0d6fbf9e37-3&btsid=0bb0622e16012917174076074ef2ae&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
