For generally slower times at
Disneyland, I'd recommend checking out touringplans.com for their crowd calendar. You'll find that certain weeks are softer than others, but maybe not a whole month at a time (except September, I guess).
If you want the highest odds of availability, the next step would be to look at which those low crowds days have the
highest points charts, or increases vs. the week before/after. Us DVCers gravitate towards low points charts, so if you want high availability you need to find days where crowds are low and points are disproportionately high.
You'll also need to be mindful of certain holidays and events. Halloween is mid-points and low/mid-crowds, but very popular for
DVC owners. Likewise for Half Marathon weekend (lowest points, mid crowds, hardest availability).
For VDH, your best bet for 7m availability is a Preferred View Deluxe Studio, which will be available at 7m a lot of the year. For PV Deluxe Studios you probably don't even need to target the relatively high points seasons. If you want other room categories, you probably won't find reliable availability when points chart is low but you might get lucky.
For VGC, your best bet is a 1BR, which often make it to 7 months, and you'll need to book right at 8am ET if you ever see it. You might find a Studio here or there, but usually not for longer stays.