No, there isn't a way to retrieve old access tokens from Dropbox. Note that you shouldn't need to, though. Any particular app-user pair (such as an app you created connected to your own account) can have multiple access tokens.
It sounds like you're referring to using the "Generate" button on the app's page on the App Console to get an access token for your app on your account. That will generate and show you an access token when you use it, but it won't give the same access token if you return to the page again later (or just refresh the page). The intent is that you would store and re-use a given access token, if desired.
In any case, creating a new access token doesn't invalidate old ones, so you can continue using old ones even if you've created new ones too.
