Ralph, most pet stores stock a "pet formula" that comes as a powder to mix with the milk. Try that (throw away any unused mixed milk, as it spoils FAST) Give it to the tyke with an eye dropper or doll bottle, maybe four or five times a day. You may have to kind of squirt it a tad to get it to suck and swallow.
Stroke the miskit with something soft while feeding it.
And here's the gross part: You will, after feeding, need to stroke its genitals with a moistened Qtip to "stimulate" the proper bodily functions.
And any body who gives me guff on this one will pay. I'm not being campy, snide, or perverted.
Good luck Ralph. It isn't easy keeping a wee one alive without the maternal unit.
If it survives one day, you're doing good.
(edited because the one-word-synonym for "Maternal unti" was censored)