Looks like Adobe have killed off Flash Player for mobile:
http://www.zdnet.com/blog/perlow/exc...on-html5/19226

Our best hope for a more recent Flash player version remains finding a device with the same ABI and libraries as the N900 and a newer flash version copying the Flash plugin from there.

That and convincing those sites that require flash to work to offer an alternative version that works in the N900 browser. (and possibly also updating the N900 browser with a newer Gecko version that supports more of the HTML5 stuff necessary to handle these HTML5-as-an-alternative-to-flash web sites)