I believe markfrom1997 meant two teleporter stones, not two sets of teleporter stones.
If you put off going to the castle for awhile (say, after finishing much of Rivertown and Verdistis) and clear out the Rivertown sewers, you can get the teleporter stones back relatively quickly after you get out of the castle.
However, you can cheat to get two sets of teleporter stones (see Lost Items - guide and directory of inventory files
), though their behavior isn't particularly helpful. Say the teleporters are labeled A and B; the second set would be A2 and B2. Whichever version of A or B you last use / move will become the dominant teleporter. If you drop A and B, then drop A2 and B2, clicking on A or A2 will teleport you to B2; clicking on B or B2 would then teleport you back to whichever 'A' teleporter you clicked on last, etc.