In my family, we do this:
Make a deck of workers using a variety of them, with the total number matching the amount the game says to include.
Make a river of cards to buy from, similar to the visitors. Usually the number of players +1.
At the end of each round, refill the river, discarding the oldest unpurchased worker before you refill.
Shuffle and recycle discarded workers if you run out. (Note - only recycle unpurchased workers. This is different than workers like the lazy peon who were removed from the game.)
We use something similar, except we make a deck of all workers excluding the Day Workers. We then have for training each round a day worker, plus a number of workers equal to the number of players (drawn from the top of the shuffled worker deck).