1. Have ICE hang out around the Food Stamp and Welfare Offices
2. Have ICE hang out any Friday or Saturday night around Walmart
3. Have ICE hang out at the local city soccer league games
4. Have ICE hang out around any landscaping business, Mexican or Chinese restaurant, or Home Depot
5. Have ICE hang out around any hospital Delivery Ward or ER
6. Have ICE hang out around any bodega or auto repair/tire shop with signs in Spanish
7. Have ICE hang out around any Laundromat
8. Have ICE hang out around any public school
9. Have ICE hang out around any police station or courthouse
Well, that's just a start on suggestions ...
You noted Walmart on Saturdays.
I would suggest that in many cities there are large gatherings of aliens at saturday flea markets. I visited one that had semi permanent stalls catering exclusively to aliens