DoubleScroll 2.1 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. DoubleScroll for Mac is included in Theming Tools. We recommend checking the downloaded files with any free antivirus.
From the developer:
DoubleScroll is a control panel which gives your Mac double arrows at both ends of your scroll bars, allowing you toscroll in both directions from one location. Requires MacOS 8.
You may want to check out more Mac applications, such as Occurrence Selector, which might be similar to DoubleScroll.