I am at WKOVR right now. We rented umbrella and two chairs through easytravelhi.com
Recommended through Tripadvisor. $30 per week. High quality equipment. I ordered on-line and paid via paypal. They drop off at your resort and pick up at no charge.
Another option to consider.....
They require a minimum of $45 for rentals in Ka'anapali
suggest to ask at the Bellhop counter - sometimes they have coolers [good for road to hana] left by guests
never asked about chairs but they might have them