There are couple of MILF affiliate programs that have solo MILF sites in their offer:
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Ethnics: American
Program:
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Pay method: check, Paxum
Promo:
Photo FHG (90), Video FHG (56)
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Ethnics: American
Fetish: Insertions, Toys
Program:
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Pay method: check, wire, wire US
Promo:
Photo FHG (46)
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Straight: Babe, Hardcore, MILF, Pornstars, Personal sites, Blonde
Ethnics: American
Program:
Extreme Bank (10 sites, CCBill AP). Revenue: 50%
Pay method: check, wire, wire US
You can check out other 700+ MILF affiliate paysites listed bellow. I'm sure you can find a lot of MILF solo sites there:
Milf Sponsors @ SignBucks.com