Hello,
Redstone (along with several other entities - for example; item frames) were removed from Creative due to them causing lag, and being used to create lag/crash plots in the past.
While I totally understand the frustration from players who have good intentions, and wish to use these items to create builds - they just cause too many issues for the moment, so I don’t see them being added back in the near future - but, possibly some day!
I may be wrong, and I have no doubts that someone will correct me if that’s the case; but I believe you can place armour stands still, you just may need either VIP+, or to temporarily purchase the perk from /shop [with in-game mana].