@winterfelllvoyager75
Someone posted a while ago they found them at
Cascadehealth.com
Monaghan does not sell them separately.
Also, note the aerobika should be replaced at 12 months and the manometer at 6 months. So this creates even more of a dilemma. Rather inconvenient.

I had a lot of conversations with Monaghan. The last person I talked to said she would pursue putting 2 manometers with the aerobika, but that has not happened.

Feel free to contact them and see if you can get better info.