I don't know if they're being discontinued or not. There has been a price drop though. See if you can get them online like here:
http://www.8thstreet.com/product.asp?ProductCode=10268&Category=Audio_Processors
I have both the Oktavas and the MXLs. In general, I prefer the MXLs on acoustic guitar but I will use the Oktavas for certain applications. From what I hear it seems that the Oktavas might be kind of hard to get ahold of these days. Bottom line though, neither one is the wrong choice.
Yeah, you can even get one of the 603s for about $75. It is my current mic of choice for acoustic guitar. That being said, it's hard to argue against the SP B1 for a first condenser mic. So much bang for the buck.
Here's a fun little exercise. Take your guitar around to every room in the house. Decide which room you sound best in and then study why that room is the best one.
Yeah, you don't say exactly what you're recording but you've got enough to get busy. Perhap another 57 or an e609 if you're doing full bands. Maybe an upgrade on the kick mic at some point? Have fun!
I have both the 603s and MC012s. In general, I lean towards the 603s for acoustic guitar. There are instances however, fingerpicking for example, where I'll use the MC012s. The type of money these things sell for is lunch money in this hobby.
FWIW I have both the 603s and the Oktava MC012s. In general I prefer the 603s on acoustic guitar but kinda lean towards the MC012s for finger picked stuff.