If you're looking for a fully-elastic waist pant for casual wear (rather than sweatpants), Falcon Bay offers this denim elastic waist pant.  Made of cotton denim, it is styled like a casual pant but with an elastic waist which can stretch to accommodate a larger size.

• Falcon Bay Platinum Plus Comfort Waist denim pants style 88-20014
• Made of 100% cotton denim
• Relaxed Fit
• Full elastic waist
• Inset back pockets as well as front pockets
• Stain resistant