I think anymore you will only find people through word of mouth recommendations.
I don't know any skilled machinists who use or have used any "services" or "apps". In fact I'd wager half the skilled machinists I know don't even have resume's.
Regarding pay, you may want to look outside your area and see what shops are paying. You mentioned your $30-$40/hr is comparable to locations in your area, but if it is just comparable, why would someone come to you? Is $30-$40/hr GOOD pay in your area?
I'll give you a point of reference. Last year I inadvertently was asked to apply at a company. That part is a long story, but I went up and interviewed. The whole time I was there they talked about how great their pay was, how great their benefits were. The best around.
After the interview they were thrilled and said they would have an offer to me first thing the following week. So my wife and I spent the weekend looking at houses online, looking at the local area, etc. Our 100 year old house was $93,000 when we bought it 12 years ago. A similar house today is $250k-$300k.
Their offer came back, and it was not great. $29/hr and benefits were lackluster, marginal, ok at best. They did give me 2 weeks vacation, which is the max they offer. They considered $29/hr excellent pay. This is for prototype/development work. I can go down the road and be a button pusher with better benefits for $33/hr.
So, while an employer doesn't care about an employee's needs as far as housing, moving, etc etc, those factor into the costs for an employee. It may simply not be feasible for someone to move and start working for you at $40/hr. Depending on where you live, $40/hr might be barely enough to get by. Where I live, housing costs are 8% below the national average. Where I would be moving to was 83% above the national average. (Similar houses cost the same in both - riddle me that) So you may be drawing from the immediate local pool, probably less than an hour drive. If your pay is comparable to the area, why would anyone leave their current shop and come to you?
I worked with guys that were called "surfers". They would leave whatever shop they were at every year, and get a $1/$2 raise. They did this every year. Some of them had a circuit they did. Some moved to whoever offered the highest. I wouldn't want to hire one of these guys.
So what is the incentive to come to your shop?