I have a lot of trouble with Pokéradar Pokémon... The best I've got was 17 Spoinks, and that was a swarm I believe. Anyway, I'm hoping to get a Roselia soon... I got my chain up to 20 before it broke. I'm doing pretty well, I could never get more than 17 before finding this guide.
@Shelcario: Check the 'cluster' and 'isolated' sections of the guide... that might be the problem. Sometimes patches on the very edges break the chain for no reason. -shakes fist- I'm chaining at the Trophy Garden.
A random peice of info that mos of you probably know, you can tell if your chain is going to break before the battle actually starts by glancing at the bottom screen, where it shows the number of Pokémon you've chained. If the number blinks away at the last second before the battle, you know you've broken your chain.
Also, I find it helps to stare at a sprite of the shiny you want to get if you get discouraged... after taking a break, of course. It motivates me. xD