Lensmate are the guys who have started offering 58mm custom built filter adapter for Canon Powershot SX10 IS camera. This was a great news for Canon SX10 IS camera owners those days. They launched it in Feb, 2009 I think. I bought a Lensmate 58mm filter adapter in April same year. Their site is pretty good and informative also they have a list of Canon SX10 IS camera accessories available in their online shop.
Their Lensmate 58 Filter Adapter is good. It fits to the lens barrel without a problem. Only problem is it's plastic. It's not a problem but you don't feel safe like a Janco 58mm metal filter adapter. But in those early days Lensmate 58mm Filter Adapter was the only one available for Canon SX10 IS camera Owners. Another problem with Lensmate is their shipping cost and products are expensive than in Amazon. I bought a Hoya 58mm CIR-Polarizing Filter which costed me over $70. Also their Lensmate 58mm adapter is not available anywhere else than their own site.
Now you can find a good 58mm Filter Adapter which is custom built for Canon SX10 IS camera from Amazon.com. It's called Janco 58mm Filter Adapter. Also there is a Chinese 58mm Filter adapter you can find in Ebay. Janco 58mm Filter Adapter is metal and its cheaper than Lensmater or Ebay Filter Adapters. Also I heard plenty of good reviews about it. So If you are looking for a 58mm Filter Adapter for your Canon SX10 IS camera or Canon SX20 IS camera then buy the Janco 58mm Filter Adapter. Unfortunatly they ship it only within USA. So you if you are not in USA you ll need to check Ebay or buy the Lensmate Adapter.