We have replaced the floor in our bathroom. We are ready to put the toilet back in place. The new floor elevates the toilet so that the old screws won't work.
Are there screws that can be found that are long enough to hold the toilet in place?
Or should we replace the old flange?

Are you trying to use the old screws? If so it is possible that the old screws were cut off after the commode was installed the first time.

You can buy new screws but if you are using a flange what you want are called "closet bolts", at one time they were different lengths but I am not sure where you would find the longer ones.

The johnnie bolts can be bought onger and are easy to insert. I am far more concerned that with this new elevation you may not be able to get a good seal with your wax ring. Measure from the floor surface to the top surface of the flange, which one is higher and by how much? You may need a flange spacer or an oversized wax ring. Back to you

Letmetellu has a point. Check to see if regular closet bolts will do the job. If not click on; Solid brass closet bolt - Shop sales, stores & prices at TheFind.com (http://www.thefind.com/hardware/info-solid-brass-closet-bolt)
To find extra long closet bolts, (see image) Good luck, Tom