Can't really advise for powder coated, but moly coated can be obtained from Bear Creek Supply, 255 gr sized to .377. They come bulked packed at 250 per box and prices are good. The only odd thing with ordering from Bear Creek is that it must be a phone order, 208-874-4322, so it helps to know what you want when phoning in. They do not have a website. I use a variety of their rifle bullets and find sizing and accuracy to be excellent. Too often I have found that standard sized and lubed bullets are under sized. The molys are not gas checked but that does not seem to be a disadvantage. You might want to Google moly coated bullets for information and what others have to say. I have a local source for the molys and the price has been about $40 for the .38-55s. They are FP in design.
LATE ADDITION:
The bulk packed is 300 count rather than 250.