Where can I get some uranium?

While having a greater amount of paragon would be helpful (although not as much as you would expect), in order to substantially boost your accelerator output you need to build both Magneto's & Steamworks. The more of each of these you have the higher your resource production will be.

Another thing which can boost your output is the religion upgrade

Solar Revolution - Accumulated faith will give a small boost to resource production

The higher your accumulated faith the greater the boost to production.

Please note that these will impact not only your Uranium production but also any other resource production

I do not know of previous game versions but as of today, each "Planet Cracker" on Dune can give you 1.50/sec.

I guess this would not exist the moment this question was asked, but it is useful for people coming back here from google.

Of course everything noted on the accepted answer is still correct as well.

I trade with Dragons for uranium. Then, just make sure the automated income isn't too far in the negative, and when you sit down to play you can make a couple of hundred trades.