For Primer don't stress over having all of the equipment details exactly right. I wouldn't buy a substitute product that you probably won't get much use of (Write in the Rain book) just to have it in time for Primer. Those products are intended to be rained on, not submerged.
I took Primer a few weeks ago, and I did not look at my Dive Rite Wet Notes during our class dives. If you have the Wet Notes, you can write the GUE EDGE predive checkout sequence, but thats about it.
Fundies is a different story. I just took Fundies a couple of days ago. During the class we learned some calculation shortcuts, and were told to write them in our wetnotes. I didn't look at those notes during the dives, but it was expected that we had them written in case we wanted to look.
I would recommend that you take steps to buy real wet notes as soon as is convenient, but don't worry if you don't have them in time for Primer.
Linda