As you've discovered, there's no button to "resend" a Quote, but there are a few options:
Send a Follow-up
This is the easiest way to resend a Quote. A Follow-up can be initiated and sent at any time by clicking into the Quote, hitting 'Actions' and selecting 'Send Follow-up'. You get the chance to preview the message before sending.
Add a comment to the Quote
You can add a Comment to a Quote and your customer will receive an email Notification containing the Comment and a link to view the Quote.
Edit the Quote
If a Quote has been sent but you need to revise pricing or conditions, you can edit and resend the Quote. Read this article about editing a Quote.
Email the Quote manually
To manually email the Quote to your customer, you can copy the Quote URL from up in the browser address bar and paste it into an email.