Actually, there's a chain retailer called Adventure Whitetip that really marks prices up and there's an actual Mares store a few hours away on Mactan Island not so far from the airport and they can get stuff and they do have people to service Mares equipment.
There are also two Spanish online retailers with very good prices who both ship (cheapish) internationally and tax free but the packages are then handed off to Philippine couriers who will have to pay import duties but they will almost always just let you pay that in cash upon delivery. Otherwise they'll contact you and give you options to pay it. Anyway they're called Diveinn and GIDIVE.
Half of Leisurepro's merchandise doesn't ship out of the US so I haven't checked with them in years. Shopee and Lazada are hit or miss on certain very popular items but generally don't carry much diving gear. Then there's Amazon which does work and will usually ship to the Philippines on most items but shipping can be quite expensive, however, they do charge the Philippine import duties right upfront and I haven't had problems when ordering from Amazon in the past such as getting shoes for my larger-than-Asian feet.
I have no aversion to ebay sellers like this.