Dennise you should try looking in the yellow pages for your area under garden centres. Several large home improvement stores have garden centres that do carry Pro-Mix HP and should have their garden centres open now. Pro-Mix HP already comes with mycorrhizae added and I add other strains when I transplant.
https://www.yellowpages.com
https://www.homedepot.com
https://www.yellowpages.com
https://www.homedepot.com