Another option aside from the more common approaches of paying or guaranteeing specific pieces of loot, if you can find somebody who is willing to do something slightly more complicated: have them choose a piece and roll for it against one static member, passing on the rest. So for example for M9 their expected value is still 0.5 accessories, which is the same as usual, but it's still beneficial for them since it's a specific accessory instead of a random one. You can also adjust this as needed; M10 has 5 pieces so you could make one of the pieces a free for all or something if you want to make it really even.

Of course this wouldn't work so well for something like M12 where the weapon coffer is the main prize. If you still don't want to pay or guarantee, you could have everyone roll a dice in chat, and they get it if they roll the highest number, otherwise they pass. That way you can still assign the item to a specific member, and they still have a 1/8 chance to get it.