There are 4 permanent mystic Altars in the world, Kharazan, Azshara, Dalaran ruins, and Silithus.
This should clue you in that you don't need mystic altars until you are level cap. You truly do not, you can completely ignore mystic enchants and still level to 60 perfectly fine with all the strength and power of an original class. Respecing at low level and trying to optimize your enchants is the same as going to the Auction house and spending all of your gold to buy new gear for your new spec. You are level 20, all you are doing is wasting your resources on a truly trivial benefit that fades in a few levels. Like if you put a talent point in the wrong thing at lvl 15. who cares, it truly does not matter. deadmines is not so heavily tuned that a missing talent point is going to make or break your lvl 20 dungeon run. Don't worry about optimizing every little thing until level cap.
Now, players who bought bundles or hit level 60 (you get a free one in the mail) can summon temporary mystic altars and usually do so in cities so if you think you need it (Again, you don't) just hang out next to the bank/call board and there is sure to be an altar pop up in a few days (when those players are nearing level cap and actually start to give a shit about optimizing, again, there is no reason to do so before level cap). it's going to cost you runes of ascension (same as talent respecs, a currency you get from doing quests/exploring/killing/etc). Runes of ascension are the same currency you spend on heirlooms for your alts and upgrading world forged items if you find one you really like and want it to level up to raid gear equivalent (the most expensive thing runes can buy)
As far as where to find Mystic Enchants, that's kind of the point/fun of this server, go explore and find them.
If you just want a guide i'm sure there will be one up if there isn't already. we found most of them in alpha, some got moved pretty late but still a decent resource:
Check out the Unofficial Reborn Collection Compendium community on Discord - hang out with 4795 other members and enjoy free voice and text chat.
discord.gg
and for world forge locations:
Explore an exhaustive and easily searchable collection of all Maps in Project Ascension. Refine your search and filter options to find exactly what you need.
cointhrow.github.io