You may also want to consider opportunities through staffing agencies like Kelly Scientific. ACS has a agreement with Kelly, but there are also other very reputable firms. In these interactions, the agreement between you and the agency should be free for you and should be non-exclusive. Never pay for this type of assistance. They should get their commission from the employer not the job seeker.
I apologize for taking so long to reply to your post. I've been neglecting to get on the ACS Network. I hope you have found something since you first posted.
As Dave noted, there are other services besides Kelly Scientific. One that occurs to me off the top of my head is Olsten. I'm sure using a search engine will provide some more. Remember, reputble agencies charge the employer fees, not the job hunter.
I also suggest you work your professional network to locate lab managers and talk to them about hiring you part-time. Perhaps you can also meet lab managers directly at ACS local section meetings.
Some firms will sign a contract directly with the individual chemist rather than working through an agency. There are advantages and disadvantages to this approach for job hunters. You will likely collect higher pay than if the agency takes a cut of your salary. On the other hand, the larger agencies often offer benefits packages. You wouldn't get these working under an individual contract with a company.
In the blog I write for Lab Manager Magazine, I've advocated that lab managers with tight staffing budgets consier hiring part-timers.
Good luck! Please post here when you find something. It will encourage others in situations similar to yours.