Did you try the lycee francais? As I know a French family who failed to get a place last year living next to an English family in Uccle, it seems there may be some picking out of English speakers for the bilingual classes in preference to French nationals who are, according the school's criteria, supposed to have priority! The website says enrolments started 10th January, you do it online, you might be too late. I'd definitely follow up an online enrolment with a few phone calls. It's the only bilingual school in greater Brussels where I'd say an anglophone child would become fluent in French with ease, as it's the only "bilingual" school which has a majority of French speakers in the French-English classes, some schools have no French speakers at all in their French-English classes! It's under 6km per year, a bargain for a private education. It's very French though, you'd have to be happy with their education system.
www.lyceefrancais-jmonnet.be/preinscription/
La Petite Ecole dans la Prairie is not the most popular of the local schools, but it's your nearest, so I'd try there first, given how late you have left it to look for a school place. It's not a bad school, just not so sought after, so is most likely of all the local schools to have vacancies. It has apparently lovely grounds.
www.la-petite-ecole.be/
Ecole communale St Job
www.saintjob.be/
Ecole Notre Dame + Wolvenberg
www.notredw.be/contact/
Ecole Plein Air - extra fees and enrolments already done, but contact them anyway
www.ecolepleinair.be/
As you're in the south of the commune, you have a slightly better chance of a place at this late stage of looking.
Remember, be persistent. I had an email today from a mum who was 40+ on the waiting list for one of the most sought after schools in Brussels, she got a place, bet it is linked to her continual following of the waiting lists.