Something is popping-up now....
Health Cabin has the tubes for the iClear30s available. Unfortunately, their shipping charges will substantially contribute to the total cost of your purchase. I found that your total order needs to be in the $100-range, before shipping, in order to be worth covering the shipping costs. The good news is the tubes are now available in multiple colors, not only in clear.
If all you need is the two tubes, you may find you are better served ordering two whole iClear30s through Fast Tech (aprox $8 each, with free shipping), and saving your spare parts.
The tubes may now be available elsewhere, but I haven't stumbled across them anywhere else, yet.
I love the iClear30s in 2.1 ohms and am considering trying to organize a group purchase directly from Innoken ($4.80 per piece), but have to order a minimum of 100 of the exact same (color and resistance) in order for them to fill the order. I have already been in contact with them, and there is no flexibility in this requirement. Given the per unit cost, it would be great, if we could organize such an order...but clearly...that would take some time. (Please let me know if anyone is interested in getting in on this, and/or has suggestions about how to organize such a venture.)
Good luck, and happy shopping. Let us know how you make out.