You can purchase an ENI directly from Tencent Cloud.
The purchasing process is as follows.

1. Log in to Tencent Cloud.
2. Click Get Started(https://console.cloud.tencent.com/vpc/eni?rid=8) to go to the ENI Console.
3. Select a region and VPC, and then click + New.
4. In the Create ENI pop-up window, enter a name for the ENI, select Network and Subnet, and configure Assign IP (select either Automatic Assignment or Enter Manually). If you want to add a tag, click Advanced Options.
   
5. Click OK.