Under Sales Tax Settings > Sales Tax Rates and Agencies, when creating NEW, you should be able to select Components you already created.
I haven't heard back from you, info23.
I'd like to make sure your that concern is addressed.
If you're trying to add a combined tax rate and components are still not populated, then let's do troubleshooting to fix this.
First, open your company using the private browser or incognito window. This will not store any web cache and help protect your privacy. Then, try to add the combined tax again and check if the components show up.
If it works, then we can go back to your regular browser and clear its cache. If not, try using a different browser such as Firefox or Internet Explorer.
I'll be around if you need more help with QuickBooks. Thanks.