The problem with most training and imaging videos (i.e., "industrials") is the tight budgets for the "little guys," and the in-place production staff (much of which is augmented by training or HR folks) for the "big guys." Carving out a niche' as an industrial video writer may be pretty challenging.
I've produced training and orientation videos since the mid-80s for (mostly) mid-sized companies and trade organizations (unions and associations) as well as government agencies and public utility companies. Not once in over 20 years have I seen a writer as a separate line item for any of these productions. It may happen on occasion, but my bet is that writers are mostly invisible except to the producers who do this type of work.
Scripts for industrial productions usually start out as poorly-written, jargon-filled clips from other documents that the client -- usually a mid-level staffer acting on behalf of a decision-maker that you'll never meet -- hopes to put video to with a voice reading the copy. The client quickly realizes that it's not going to happen with any kind of good results ... thus begins the education process, facilitated (usually) by the production house.
The house will sit down with the client and consider the realities, offer a price range, then assign a producer (or production contact) to oversee the project, which goes forth from there.
Unfortunately, these projects usually turn out to be poorly-written despite the re-crafting of the material ... even more poorly-worded than this sentence, if you can imagine that.
- [SIDEBAR: Ever fallen asleep watching a training program? Although many elements affect how well it connects with a viewer, the primary factor in effective dialog writing is whether it's written for the EYE or for the EAR. Most people write for the EYE. Very, very few writers know how to write for the EAR. Makes a HUGE difference.]
A really good scriptwriter would add great value, not only to the final result, but as a means of reducing production costs.
The costs rise and fall with the script ... and with the writer's and/or producer's understanding of the production process. The problem is, you're mostly dealing with clients who are uneducated about the production process AND with video producers who are trying to maximize the small budgets they're lucky to be working with.
Here's the bottom line: If you really want to supplement your income with industrials, you need to discover more about the entire production process beyond the video-audio/2-column format with appropriate production shorthand, to the point where you can offer your services as a producer. Producers coordinate with the client, draft the script, and supervise shooting and editing (those are the basics, at any rate). If you don't have a good grasp of the whole process, your effectiveness as a writer will be greatly limited.
It can be very lucrative, but unfortunately the market and its players aren't really set up to hire industrial writers as standalones. But if you're still determined, my best suggestion would be to work with producers ... which is what it sounds like you're trying to do.