East Tennessee is not the "great hinterlands", you are not that far for a couple bonsai orientated nurseries, including Bjorn Bjornholm and Owen Reich. It is possible to pick up modern substrates for creating modern bonsai soils. American Bonsai, & Stone Lantern, both do mail order if the time it takes for a drive is not feasible.
Pebbles, do not hold water well, and they are heavy. Pebbles and compost is a 1850's to 1930's style bonsai soil, and if you look at show catalogs from those days, you can see bonsai was much more primitive then, trees today have a much greater development in ramification and style. In part this is because constant problems with the old soil mixes were constantly setting back development of the trees. Modern substrates allow less frequent repotting and much more resilience in vagaries of weather.
Modern substrates are varied, but usually contain a lightweight, porous particle like pumice or perlite. Also used is crushed and sieved lava, as it holds less water than pumice. In addition often use a unique form of clay derived from erosion of volcanic tuft, akadama and kanuma, which are often imported from Japan. Similar deposits occur in the Pacific Northwest, but are not currently being mined. This volcanic clay, akadama, has properties that clays derived from glacial till simply do not have. For those who are price sensitive they use a USA sourced calcined clay (clay fired to retain shape, like crushed brick particles)) or fossilized diatomaceous earth (note this is not the powder, but hard gravel like chips of rock made of silica from diatoms). There are other ingredients used, many developed by the landscape plant industry.
The "gold standard" mix used by many high end bonsai artists is akadama, pumice and lava, in roughly equal proportions for conifers, increasing the akadama portion for water retention for deciduous trees.
Another successful mix also used by some is pumice, and douglas fir bark chips, at roughly 2 to 1 ratio.
There are many other mixes that work, I know it is a slogg, but read through the following thread, the take away is that there are many soil components that can work, but really the best ingredients are Pumice - any mix based on pumice has a good chance of working well long term for raising bonsai.
Perlite is a "almost good enough" substitute for pumice in training pot phase of bonsai. Perlite is just too light to be used in a small display bonsai pot.
Akadama has a difficult to argue with track record for producing excellent root systems. (especially combined with pumice).
The last is ignore any "soil wars" exchanges that get too heated. Not meant to offend, but some have very passionate opinions about how to grow their bonsai.
Questions about soil physics come up all the time and I find that I repeat myself a lot on this topic. I'm going to try and write a reference for folks to refer to on this topic. I'm expressly NOT going to offer you any advice on what soil you should use in your garden, whether you should use...
www.bonsainut.com
So while you can raise a decent tree in the antiquated mix that you are proposing, using modern substrates will make your horticulture easier to master. Nothing wrong with composted pine needles. Actually the pebbles is the part of your mix that makes me cringe, the pine needles are a "good thing" in moderate amounts.