Sorry! I only just noticed this. I have some little 3mm rare earth magnets from eBay and are just fine! I can happily hold up the whole model from just the rider with no fear of them splitting.
I just started working with magnets as well. The work great for connecting a Howdah to the older Stegadons... I was hoping that I would be able to magnetize some hands and weapons for my Oldbloods, but the magnets I got (not sure of the size, but my guess would be 3mmx1mm) are larger than the modeling drill will allow for, as well as a it too large for comfort when I start drilling into the arms of my units... seems like I an going to loose too much plastic. Anybody know where to get some good 1mmx1mm Rare Earth magnets?
RareEarthMagnets (I think that´s how they´re called), they only ship to the US for reasonable prices, if you want them in Europe you´ll have to pay an extra of around $70 Edit: After a fast search I didn´t find the website, maybe I got it wrong. Search ralf137 in youtube, he´s got a series of WH40K advanced techniques, and one of them is about magnetizing, he names the brand there. But it is the US-only brand I mentioned above Edit 2: found it!