You can get off-the-shelf DC-DC converter modules, often these are unregulated, and *can* be quite noisy, have fairly poor regulation, but isolated. It can be common practice to follow the output of these with a linear regulator, even a cheap 7809 (as you mentioned) will do, as this can clean up the line and provide short-circuit protection. An example would be 12V in 12V out DC/DC module, with a 7809.
The 250mA output current means 9*0.25 = <2.5W, but I would go for at least 4W for headroom. Aside from digital/multieffects or boutique reverb pedals, most draw very little current. I suppose if you can get them cheap enough you could use one DC/DC module per pedal output, in which case you could go with the lower 2W.
If you're ordering from Farnell or Mouser, I would buy a few from different manufacturers (if they're fairly cheap like $4) just to test them and see how noisy they are - the noise on the output can be sorted with a regulator and/or filtering, but EMI, radiated noise, would require shielding so is harder to sort.
There are indeed IC's designed purely to provide isolated low voltage supplies, often just simple push-pull oscillators, but the transformers they are designed for can be difficult to source. Also I can't see to find any part numbers. As this isn't for high volume, I would go with modules.