If you can't find any other perlite the MG is okay if you wash it well first. That will remove most of the slow release nutes. Check nurseries and garden centers. You'll have a better chance of finding it there than you will in the big box stores.
Lamberts seems to make good products and I know others here have used it to good success. I would recommend using it straight for seedlings and for your final pots mix it with 25% worm castings and then add 50% perlite to that. I've tried that Black Cow manure it's fairly worthless. The castings will give better results. The Lamberts does have dolomite lime included but with the worm castings you may need to add a bit more to balance your pH. I would suggest you make you mix, wet it with pHed water, let it sit for 3 days, then test the pH. I would also suggest adding some mycohorrizal fungi to the mix. I used Humbolt Myco Madness but others here prefer Great White. Both are good.