From memory the real PRL100 is about a 1000m of ascent in total.
There are also event only routes such as the Watopia Waistband, which should give you around 600m for 100 miles. There are group rides for the whole 100 miles which give you the benefit of some draft and camaraderie with your fellow sufferers. Check the route at Zwift Insider:
Have a look at Zwift Power for suitable rides, for example:
Although these may not completely suit your date and time. You can filter to find suitable events.
If you go solo, personally I’ve used Tempus Fugit for long rides. Usually its busy with plenty of others and easy to find a group to share part of the journey with. Also the new French routes should be available in August. A route such as RGV might work.
Other suggestions would be to join multiple group rides. Often a sub 2 group ride (steady pace for a long ride) on a flat course will cover around 33/34 kms for an hour. If you can find a few rides and free ride in-between this might work, but it won’t show as one ride in Strava etc.
Don’t forget that there is a 100 mile black jersey to be unlocked, so keep going until you get the unlock, I think its at 162kms.
Good luck and ride on.