Olaparib is covered under the PSHCP (public service health care plan) for non-BRCA mutations (such as PALB2) and even for BRCA-negative, if prescribed; no documentation is necessary. The plan covers 80%, there's a maximum $3000 annual co-pay, then the rest is covered 100%. So, for people in your situation, try to get a job at the federal government or have your spouse get a job there. Here's the eligibility criteria: https://www.njc-cnm.gc.ca/directive/d9/v9/s67/en#s67-tc-tm_1
Note that the PSHCP will cover only up to $8800.26 for the prescription and dispensing fee, as that's the limit for "reasonable and customary charges". Note that if you can pay in cash (with a cash back credit card,), you can get a 20% discount through Astra Zeneca's patient support program if you use the mail-order Bioscript pharmacy (Astra Zeneca's patient support program has just changed to Bioscript from Bayshore.)
What's your pharmacy / How did you get it for only $4300? I know that pharmacies can charge whatever they want; Shoppers Drug Mart charges $9409.45 for a full dose (600 mg/day) (note that's $500 over the max price covered.)
The oncologists speak highly of Olaparib, as it extends PFS for two years or more; they think it's much better than letrozole as a maintenance option.
Olaparib is also available in India as "Olanib" for about $1000/month for 600 mg/day. If you have Indian friends with contacts in India, they can perhaps find you a trusted pharmacist who can get it for you.