Those five names you mentioned are good posters in this great community, I don't know if they will accept this offer you brought, because there are some of them who don't like wearing the signature campaign while there are some who are wearing signature campaign right now
If they are users who don't want to wear paid signatures, you can not hire them.
If they are opened for wearing signatures, a company has to consider some important things. For example, what are their favorite boards and whether their favorite boards are matched with your company products.
If your company has products that are technical like a wallet, you will find users who are actively and have deep knowledge in technical things.
If your company has products in gambling, you will find posters who are actively in gambling.
Sometimes if you want to localize your campaign, you will find best posters in your target local boards.