It is not necessary to find the queen to do an artificial swarm, although it is probably safer if you do. If you can't find the queen do this:
Put a new brood box of foundation on the old site, leave a gap of a few frames in the middle.
Then go through the old brood box and chuck/brush all the bees into the new box. When they are all in add the remaining frames plus a frame of open brood to act as a draw to keep the bees in their new home and as a trap for varroa.
Put a queen excluder on top and then the old brood box, after removing all but one queen cell - I've left two and they have swarmed as well. After a couple of hours the nurse bees will have gone up into the old box and this can then be taken away and set up close by.
Adding a queen excluder under the new brood box of foundation helps keep them in for a week.
You can remove the frame of sealed brood you left in and destroy it after the brood has been sealed. This will knock back the varroa. Alternatively, if you are not using a bait frame, you can treat them with OA syrup tstraight after the re-housing because being broodless this will be effective.