Usually a franchise dealer can not sell aftermarket parts for the franchised brands
SO a Toro dealer can not sell aftermarket Toro parts
Add to that Toro ( or any other maker ) may refuse to supply parts to a distributor if they also distribute after market parts for their brand.
So for instance I can not get many aftermarket Kohler parts any more because my distributor sells genuine Kohler parts .
Prime Line ( one Star forgot ) sell a lot of Kohler aftermarket parts but they left Australia 10 years ago so I can only get Prime Line parts retail .
All of the after market parts distributors have a "find a Dealer" option to find a dealer near you .
Big on line retailers like Jacks Small Engines or Parts Tree or Pro Parts are all in a similar boat
For them it is worth more money to sell the complete range of genuine parts rather than make a higher mark up on a smaller range of aftermarket parts .
Jacks , Pro Parts , E-replacement , Parts Tree , Messicks are all places I get parts from because they all seem to charge different prices for the same item and none of them are cheaper overall
And some times the aftermarket part is more expensive than genuine parts .
FWIW
Locally I have 2 wholesalers , 5 retailers ( get discounts from 2 of them ) plus the USA ones listed above I buy regularly from.
I also buy from 5 factories direct from China and one in Hong Kong ( although Dave does not seem to be there right now ) plus a distributor in China .
There is no single supplier that carries all of the parts and none that have the best price on everything .
I buy from people who sell good quality parts ( net necessarily the cheapest ) because I have to offer warranty on my repairs ( 3 months is manditory down here )