Sythe is definitely your best bet. I have followed the community around them for years and now that there is now an actual forum for the threads, it gets quite popular in comparison to elsewhere. I personally do not recommend buying names nowadays, however. Recovering them is quite an easy process to complete and Jagex does not currently have the tools to specifically decline players whom do; whether sold or not - In a nutshell. Infinity and Balance usually talk the most about this on the RSOF, so you can find similar quotes there by visiting their forum profiles. The company is constantly changing their rules as of late; display name distribution and management being a massive grey area.