Hi, fortune 200 employee here

Each company has its own procurement process for contractors so ymmv. It's challenging to get a foot in the door at Enterprise orgs because there are typically a few factors that you might not think of if you haven't already done work for them.

1. the people making selections have to know you exist. This is frequently achieved via direct contact: calling or emailing with a free demo of your product or service. You may not always be talking to the person who makes the decisions but you might find mid- to senior-level engineers or managers who can influence the decision. Presence at tradeshows is also a big way to get exposure. Knowing people in the org can be a huge advantage
2. there are invisible standards you might have to meet. Often procurements take months to years to work out with legal, privacy controls, and architecture standards evaluations. We just hired a company to deliver some imagery over a 3 month period and the contract took almost 3 months to get resolved. You may need to carry special types of insurance depending on the industry of the company that would hire you. One company I worked for had a list of approved vendors at varying statuses of what they could and couldn't work on.
3. for the reasons above, it's usually wise to have a dedicated sales person who can make contacts and schedule demos, may already know people in the industry, and knows how to work those contacts into referrals. This person ideally also knows how to navigate the corporate/regulatory framework to make sure you have the right secret handshakes.

Hope you find this helpful and good luck

I have a couple large customers (as in $billion+ companies) and I got the contracts because I knew people at the company, or knew someone who knew someone. Remember the foundation of business is trust. Getting a referral is basically a shortcut to them trusting you. If you then go on to do good work for them you can get a very good thing going for yourself.

I’m responsible for appointing contractors for all types of work, including this.
I hire people I know or, if it’s a new area for me, based on recommendations from colleagues or my network. Only if I don’t know anyone and don’t get suitable recommendations do I look at the market and ask for quotes. People do business with people, not companies. I have used the same external IT team in my last 3 roles. I know that makes it difficult, but best bet is to build on existing relationships and forge new connections