Your search for "isr4451" revealed the following:
Cisco ACS-4450-FANASSY Fan Assembly for ISR 4450 and 4350 Routers
SKU: NSB-2138
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 79.99
• Only 2 remaining
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Cisco MEM-4400-2G 4451-X ISR Series 2G DRAM Router Memory
SKU: NSH-7670
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 69.99
• Only 2 remaining
Call if you need more
NEW Cisco ISR4451-X/K9 4x 1GB RJ45 4x SFP 6x Slot (3x NIM 2x SM 1x ISC) Router
SKU: NSN-8280
Condition: New
Shipping: Overnight Options
Warranty: 365 days
NEW Cisco MEM-4400-2G 4451-X ISR Series 2G DRAM Router Memory
SKU: NSN-5425
Condition: New
Shipping: Overnight Options
Warranty: 365 days
Cisco PWR-4450-AC-2 ISR 4451-X 450W AC Router Power Supply
SKU: NSH-8031
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days