rockm

"Keep the bark percentage low, because it can take nitrogen away from the roots when it starts to decompose."

A myth. The decomposition of the bark isn't enough to starve roots of nitrogen, especially if you're using water-based fertlizers regularly. I think Brent pointed that out a while ago if memory serves. The problem is more to do with the structure of bark. It will break down within four or five years as it decomposes. If you use too much in your mix, the soil breaks down and loses drainage over time, where a completely "soil less" mix retains its structure far longer.

You have to be careful about chicken and poultry grit in coastal areas and states. In the south, oyster shells are ground up and used for grit. Oyster shells are inappropriate for bonsai soil as they are calcium, basically. They will make your soil too basic (as opposed to acidic). "Granni-grit" is ground up granite and is the brand name that's most common in feed stores.

For sand, I use swimming pool filter sand. It can be found at swimming pool supply stores--the stores around here stack 50 lbs bags of it outside in the parking lot. Mystic White is the brand available to me. It's alot coarser than play sand and is crushed quartz, extremely angular and it does not break down.

Avoid pea gravel of any size at all costs. It is NOT a good thing to have in bonsai soil. Since it is rounded, it compacts and as it is basically non-porous, it has no ability to "store" moisture or fertilizer--two critical things for soil components.

The option for organics can be solved using decomposed pine bark soil conditioner. "Nature's Pride Soil Conditioner" is what I buy at Home Depot. Soil conditioner is used to break up clay soils and make them more permeable. I would be surprised if it's not around in your area.

Additionally, if there are specialist orchid retailers in your area, might be worth a visit. There are more than one grade of orchid soil. The main soil is simply too much work to break down into smaller pieces.