Our villain is a telepath and mind-reader that my players wish to be able to lie to and prevent from learning their plans. The villain is homebrew and essentially has an ability that is innately and permanently activated for all creatures around him. He can read what everyone is thinking at that moment, detect lies, and communicate telepathically.
Mind Reader: you can read the thoughts of any creature within 20 feet of you, with at least 4 Intelligence, that speaks a language you understand, and is not protected by a thick barrier. You hear their thoughts as if they were talking aloud, so you can determine that invisible creatures are around you, and eventually locate them. Their thoughts do not interfere with your regular listening skills, and are not affected by loud noises either. You hear both distinctly and separately.
How can these PCs lie to the villain, and keep the villain from learning their plans by reading their thoughts? I came up with 2:
Mind Blank - one willing creature you touch is immune any effect that would read its thoughts,
Ring of Mind Shielding - you are immune to magic that allows other creatures to read your thoughts
Other spells, like Nondetection or Private Sanctum shield you against Divination spells, which this Telepathy ability is not. Class features, like the level 17 Rogue's Soul of Deceit [SCAG], are not really applicable.
However, this essentially means that either our Bard is going to have to learn Mind Blank, or they need to go find a bunch of these rings. This isn't necessarily bad, but the Bard isn't the most reliable player, and scavenging for 6× the same item that permanently protects you seems boring.
Are there other options to do this? Preferably consumables that they can hire people to craft for them, like potions or scrolls (that can be activated by anyone), or an item that protects the entire group simultaneously?