I have been shopping around for Duplo plates this week to no avail.
I know they exist, but fed up with searching I made this for our son.
I printed this in ABS on an Up! with 0.3mm layer and loose fill, normal settings in about 1,5 hours. It fits very well.
It's quite bendy, so probably going to glue it onto a small wood plate for more stability.
No idea about de-lamination or nobs breaking off, so as always with home-printed toys that could potentially break or produce small parts:
Use at your own risk and only allow children to play with this under close supervision.