BFO-9000 from Keeb.io,you can make a single plate to hold both pcbs side by side for up to a 6x18 grid,you can remove up to two rows/columns from each to drop it to a minimum of 4x14.
Imagine this as a single plate-
That one is mine,here is a single plate version I saw on Reddit a while back with Kailh Choc switches-
Also this one as well which is Cherry MX like mine-
You would need to source your own switches and keycaps and solder everything together. You can design your layout in
http://www.keyboard-layout-editor.com/#/ and then copy the raw data over to builder.swillkb.com to create .svg's that you can use to have custom plates cut from.
It is so satisfying to type on a board you assembled from all your own chosen parts.