where can i find a download for a macbook pro ios11 please

Terminology. There is no iOS11 for Macs. It is macOS 11 (aka Big Sur) and your ability to upgrade to it is dependent upon the year and model of your MacBook Pro. You can determine that from Apple () menu : About This Mac panel. Compare that product description line content in parenthesis to the following:

See: macOS Big Sur is compatible with these computers - Apple Support

and if your Mac is compatible, then you can download the full Big Sur installer:

How to download and install macOS - Apple Support

Note that macOS 11.* only supports 64-bit applications and many of the applications you are currently running on macOS High Sierra may only be 32-bit. Run the free Go64 application to get a list of your 32-bit dependencies and then check with those vendors to see if they now offer 64-bit versions compatible with Big Sur. That includes your printer and scanner vendors drivers.

Never perform an upgrade without a current Time Machine backup of your Mac.

Exactly what file are you wanting to download ... complete file name plus extension.