I can't believe noone had any real suggestions...
You can still buy resistance bands and anchor them to the floor and wrap over your dumbbell as you press, increased load immediately.
You can attempt the same thing with chains, I would recommend this.
Now if you are really comfortable with being creative you can attempt to strap a weight plate to your 50lb dumbbell. Again, it may seem crazy but it can be done, here is an example image where they strapped mini weights to a dumbbell, that seems much harder though. I'm saying strap a 45lb plate on the dumbbell with a strap or rope, it's not impossible.
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Desperate times, desperate measures.