Unfortunately the only source for that software was Cisco. And as Marvin points out Cisco stopped making that software available a long time ago. There is no open source software for the 3600 routers. I am not sure what is the problem with setting up this router. But a software update does not seem to be a realistic solution for this problem
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Xiaomi AIoT Router AX3600 is up for pre-sale in China for
TL-WDR3600 | N600 Wireless Dual Band Gigabit Router | TP-Link N600 Wireless Dual Band Gigabit Router. Blazing Fast Speeds. With one Gigabit WAN port and four Gigabit LAN ports, the TL-WDR3600 is able to support a robust and extremely fast wired network, ideal for latency-sensitive applications such as HD media and online gaming. Working: Cisco 3600 3640 Switch IOS image for Gns3 Download
Makita 3600BR
Part Numbers for the Cisco 3600 Series Routers Cisco 3600 Series Products : Cisco 3600 2-slot Modular Router-AC with IP Software: CISCO3620: Cisco 3600 2-Slot Modular Router-DC with IP Software: CISCO3620-DC: Cisco 3600 2-slot modular router, use w/ AC RPS with IP Soft: CISCO3620-RPS: Cisco 3600 4-slot Modular Router-AC with IP Software: CISCO3640: Cisco 3600 4-slot Modular Router-DC with Huawei AR3200/3600 Series Router License Price