Cannot Find ADSL Firmware 4.0.0.18 for Cisco 1801

I have a number HWIC-1T     of Cisco 1801 routers connected to BT UK’s ADSL2+ Annex-A Wholesale Broadband Connect [WBC] services. The routers are experiencing connectivity issues. There is a cisco product bulletin that defines v4.0.0.18 as the version of ADSL Firmware required on the Cisco 1801 when connecting to this BT service.

I would like to upgrade the ADSL Firmware for these routers but I  cannot find v4.0.0.18 for the Cisco 1801 on CCO. All the 4.0.0.18 downloads appear to  be for various flavours of 800. The Cisco product bulletin shows the 1801 as having the same chipset as the 857,867,877 and 887. Can I use the Firmware from one these 800 models? The MD5 Hash for the code suggests all of the these 800 model use the same code?

Has anybody seen this problem with the Cisco 1801 or upgraded the Firmware to 4.0.0.18.

 Yes, the 1801 use same HW and FW as the 800 and the WS-X45-SUP7L-E