This August for 9 days from the 8th to the 16th there is a special Takara Tomica event being held at Pacifico Yokohama. Not only can you see how the factory operates, but the kids can make cars and play with plarail.
Cost: Tickets bought in advance cost 900 yen for school age children and adults, 700 yen for age 2 to 6. Tickets bought on the day cost 1000 yen for school age children and adults, 800 yen for kids. Children under 2 are free.
Time: You can enter anytime between 10am and 4pm.
Place: In English – https://www.pacifico.co.jp/english/index.html
PHONE # for booking: 03-5435-0604. MOnday to Friday. It doesn’t specify they have English speakers, but its worth ringing to see.
Access and further details (Japanese only): https://www.takaratomy.co.jp/event/eventlist2/tomica2015-yokohama.html