Personally, this was the very first time I ever had the Welcome Wagon show up. I've played the Strangerville scenario three times, now. I like to wait awhile in between as it can be very intense when you face-off with the Mother. Plus, I like that I forget much of what must be done, so that it's like new. I would just place a house in Strangerville, mark it rental and have your Sim take a 1-2 day vacation there. You may be lucky enough to have the Welcome Wagon show up. Or, you could temporarily move your Sim there using the freerealestate on cheat. Stay long enough for the WW to arrive and then see if the MIB show up. Play around with it, have fun. :)