Spidermite Infestation 1 week to harvest

I've never had spidermites before and 2 weeks ago I put a UV Reptiglo 10 lamp
over the plants and thought the leaf spotting was from the UV light being too close.
1 plant, a Jorges Diamond is 9 weeks into 12/12 and while checking the trichs I saw the damage, 2 plants next to it are also infested.
I have 21 plants in a 2x2x2 metre mylar grow tent and the 3 infected plants were in the back corner and I cant get to them without taking all the plants in the way out of the tent, which is why I didn't pick it up 2 weeks ago when I first noticed the spotting on the leaves, plus I thought it may have been UV damage.
Any suggestions on what to do, I think it might be too late to spray as it's so close to harvest.
The other 2 affacted plants are 6 weeks into 12/12 so I sprayed them.
Thanks.

Also this bit of info from the discription-
(The strain is almost maintenance free, also spider mites and other pests know to leave Jorge’s Diamonds #1 alone.)
Strange how nearly all the mites are on this particular plant.

The plant might have a missing gene or two from the original strain thus losing it's 'immunity' from spider mites... I assume you isolated the few that are infested? I purchased predator mites back in the day via the web and had them overnighted to me. What a waste of $50... I'd do one of a couple of things:
1) We have ladybugs galore here right now. You can spend a few minutes outside collecting them and bringing them in, I assume they eat mites too.
2) Go to a local grow shop/hydroponics store and they might have some predator mites that are actually alive...either that or the owners/employees might have some.

My 1 and a 1/2 cents...

Yeah dude, get some predators, you can use neem oil but will increase chances of mold. I would spray and make sure you have some air blowing so it can dry.

I have isolated the 3 infected plants, they are now downstairs in the garage.
Even though I've never had mites before I bought some Dead Red a while back and sprayed them with it, it's specificaly for spider mites.
There is 1 store on ebay that sells predator mites but it will take about 10 days to get them. I'm in Australia and it's winter, and I live in a townhouse with no garden so there's no way I can collect lady beetles.
Thanks for the replies.