if you have access to the knowledge base try this link  

https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=59807&sliceId=2&isLoadPublishedVer=&docType=kc&docTypeID=DT_DOWNLOAD_1&stateId=15781&cmd=displayKC&dialogID=577016&ViewedDocsListHelper=com.kanisa.apps.common.BaseViewedDocsListHelperImpl&openedFromSearchResults=true

you can get a trial version of sage 50 CA if you don't have it 

http://www.sage.com/ca/sage-50-accounting/try

For some reason it keeps telling me I am not authorized to view that document

I already have both Business Visions 2019 and Sage 50 accountants edition 2021.2 installed on my computer

you have to login on the to your sage customer portal  account on the upper right on the page that gives you that message 

I did and it still says I'm not authorized

did you create a portal account?

this is different than sage city 

I have a sage city account and a partner portal account 

try to find the this knowledge base number KB 59807 to access the download in your portal account 

Hello all,

It appears that KB (59807) - Sage BusinessVision to Sage 50 - CA Edition Data Migrator was archived back in December 2020 as this product is no longer being sold. DebHawkins happy to set up a callback, just let me know. A Sage BV specialist would be needed, to chat with an agent go here, you'll be greeted by the AI Pegg and then connected to a Sage BV support rep. 

Warm Regards,
Erzsi