Your search for "MEM-4" revealed the following:
Cisco MEM-4400-4GU8G ISR4400 Series 4G to 8G DRAM Upgrade Memory
SKU: NSH-7672
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 112.99
• 7 in stock
Call if you need more
Cisco MEM-4300-4G ISR 4000 Series Router 4GB DRAM (2G+2G) Memory Module
SKU: NSH-8514
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 69.99
• Only 2 remaining
Call if you need more
NEW Cisco MEM-4300-4GU8G ISR 4000 Series Router 4GB to 8GB DRAM Memory Upgrade
SKU: NSN-7351
Condition: New
Shipping: Overnight Options
Warranty: 365 days
Cisco MEM-4300-4GU8G ISR 4000 Series Router 4GB to 8GB DRAM Memory Upgrade
SKU: NSH-7669
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days